Walk into any Fischer's lovebird breeding room and you will find at least one bird described as "darker than normal." That darkness almost always traces back to a single mutation: Dark Factor. It is one of the most widely present mutations in the hobby — often carried without the breeder even knowing it — yet it is also one of the most consistently misunderstood. Many breeders believe Dark Factor adds extra melanin to make the bird darker. It does not. And many assume you can carry it invisibly as a split. You cannot. This guide covers exactly what Dark Factor does, the six colour forms it creates, how to predict offspring, and the common mistakes to avoid.
Mechanism: Spongy zone narrowing in feather microstructure — NOT extra eumelanin added
Mode: Autosomal dominant incomplete (codominant) — one copy shows, two copies show more
No splits: Every copy of Dark Factor changes the bird's appearance. There is no hidden carrier form.
Six colour forms: Light Green, Dark Green, Olive (green series) · Blue, Cobalt, Mauve (blue series)
I use the narrowing of the spongy zone as an in-hand identifier rather than waiting for photographic comparison under strong light, the back-neck feathers of DF birds show a noticeably tighter, denser structure that single-factor and wild-type birds simply don't have, and it's consistent enough to call confidently at banding.
What Dark Factor Actually Does — The Spongy Zone
The colour of a lovebird's body feather is produced by two systems working together. The first is pigment: eumelanin (the dark melanin in the feather barbules) and psittacofulvins (the yellow-red pigments unique to parrots). The second is feather microstructure: a layer of sponge-like cells called the spongy zone (or medullary layer) that scatters short-wavelength light, producing the structural blue-green colour you see even before pigment is applied on top.
Dark Factor does not touch the pigment system. It has no effect on how much eumelanin or psittacofulvin a bird produces. Instead, Dark Factor narrows the spongy zone — it physically compresses the light-scattering layer. When the spongy zone is narrower, it scatters shorter wavelengths (shifting the structural colour toward blue and away from green-yellow), which makes the overall plumage appear denser and darker.
This distinction matters enormously for predicting combinations. Because Dark Factor works on feather structure — not pigment — it interacts with every pigment mutation (Blue, Opaline, Cinnamon, Dilute, etc.) in predictable, additive ways without altering those mutations' own effects.
Dark Factor does NOT add extra eumelanin. It does not increase melanin production in any way. The darkening effect is purely structural — a narrower spongy zone shifts the optical output of the feather. Understanding this prevents a chain of wrong predictions: e.g. "Dark Factor on a Cinnamon should grey it out" — wrong, because Dark Factor does not interact with the TRP1 gene that Cinnamon affects.
SF vs DF: The Six Colour Forms
Because Dark Factor is an incompletely dominant mutation, each copy adds an incremental effect. Zero copies = normal. One copy (SF = Single Factor) = a darker bird. Two copies (DF = Double Factor, the homozygous form) = an even darker bird. This creates a three-tier progression within both the green and blue series.
Light Green
The normal wild-type colouring. No Dark Factor present. Bright, vivid green with full orange-red face mask.
0 copies of DFDark Green
One copy of Dark Factor on a green background. Visibly darker and more saturated than Light Green. Face mask colour unchanged.
SF · 1 copy of DFOlive
Two copies of Dark Factor on a green background. Substantially darker — often described as olive-khaki or dull yellow-green. Most extreme green-series form.
DF · 2 copies of DFBlue
The standard Blue mutation with no Dark Factor. White face, clear cobalt-to-blue-green body. Base of the blue series.
0 copies of DFCobalt
One copy of Dark Factor on a Blue background. The spongy zone narrowing deepens the blue considerably — richer and darker than standard Blue. Highly prized in show birds.
SF · 1 copy of DFMauve
Two copies of Dark Factor on a Blue background. The deepest, darkest blue form — often described as mauve or purple-grey. Striking but harder to breed to standard.
DF · 2 copies of DFInheritance — Why No Splits Exist
This is the point where many breeders get confused, especially if they are used to working with recessive mutations like Blue or Pale Fallow where a bird can look normal while secretly carrying a gene copy.
Dark Factor does not work that way. It is dominant — meaning it always has a phenotypic effect when present. Unlike a fully dominant mutation (where one copy looks the same as two copies), Dark Factor is incompletely dominant: each copy incrementally darkens the bird. The result is that you can always tell from looking at a bird how many copies of Dark Factor it carries:
- Normal Light Green or standard Blue = zero copies. No Dark Factor at all.
- Dark Green or Cobalt = exactly one copy. SF Dark Factor.
- Olive or Mauve = exactly two copies. DF Dark Factor (homozygous).
There is no "split for Dark Factor." A bird either shows it or does not carry it. This makes Dark Factor one of the most transparent mutations in the hobby — you can read the gene dose directly from the bird's colour.
With a fully dominant mutation (like some Pieds), one copy and two copies look identical — so you cannot tell homozygous from heterozygous by eye. With a fully recessive mutation (like Blue), zero copies and one copy look identical — so splits are invisible. Dark Factor sits in the middle: each copy has an additive effect, giving three visually distinct forms (Light, SF, DF) that map directly to zero, one, or two gene copies.
Core Pairings
-
25%
Light Green (no DF)Zero copies — normal wild-type green
-
50%
Dark Green (SF DF)One copy — same as parents
-
25%
Olive (DF DF)Two copies — darkest green-series form
-
50%
Dark Green (SF DF)One copy — same phenotype as DF parent
-
50%
Light Green (no DF)Zero copies — no Dark Factor inherited
-
100%
Dark Green (SF DF)Every chick gets one DF copy from the Olive parent — all show SF Dark Factor
Calculate your Dark Factor pairings
Combine with Blue, Opaline, Violet, Cinnamon, and moreDark Factor + Blue: The Colour Ladder
Dark Factor and the Blue mutation are on completely separate gene loci and combine independently. This means a bird can carry any combination of Blue and Dark Factor doses. The result is a clean two-dimensional colour ladder with six distinct named forms — three in the green series (varying by DF dose), three in the blue series (also varying by DF dose).
Green series — Dark Factor dose
Blue series — Dark Factor dose
| Colour name | Base mutation | Dark Factor dose | Appearance |
|---|---|---|---|
| Light Green | None (wild-type) | 0 copies | Vivid bright green, orange-red face |
| Dark Green | None (wild-type) | 1 copy (SF) | Noticeably darker, more saturated green |
| Olive | None (wild-type) | 2 copies (DF) | Olive-khaki, dull yellow-green, darkest green form |
| Blue | Blue (B1 or B2) | 0 copies | White face, clear blue-green body |
| Cobalt | Blue (B1 or B2) | 1 copy (SF) | White face, rich deep cobalt-blue body |
| Mauve | Blue (B1 or B2) | 2 copies (DF) | White face, very dark mauve-blue or purple-grey body |
The show bird combination: SF Violet Dark Blue (Cobalt-Violet)
When Violet is added to the equation, the ideal show bird combination is widely considered to be Single Factor Violet + Single Factor Dark Factor on a Blue background — commonly written as SF Violet Dark Blue or Cobalt-Violet. The Violet mutation in the presence of SF Dark Factor on Blue produces the richest, most saturated violet-blue expression. DF Dark Factor (Mauve-Violet) tends to appear too dark and muddied, while standard Blue-Violet (no DF) lacks the depth of the cobalt base. SF Violet on SF Dark Blue (Cobalt) hits the ideal balance.
Common Mistakes and Misconceptions
Dark Factor works on feather microstructure (spongy zone narrowing), not on melanin production. It has no effect on eumelanin quantity. Thinking it adds melanin leads to wrong predictions when combining with Cinnamon (which reduces eumelanin) or Dilute (which affects macromelanosomes).
There are no splits for Dark Factor. Zero copies = Light Green or Blue (no effect). One copy always produces Dark Green or Cobalt. If a bird looks like a normal Light Green or Blue, it carries zero Dark Factor — not one hidden copy. Incomplete dominance makes every copy visible.
Pairing two SF Dark Factor birds produces 25% Light Green, 50% Dark Green, and 25% Olive. Breeders are often surprised to get Olive chicks from two Dark Green parents — or to get Light Green chicks that appear to "revert." Both outcomes are expected from basic Mendelian ratios for an incompletely dominant trait.
All three produce greenish-yellow or olive-toned birds, but the mechanisms and health implications are completely different. Olive is two copies of Dark Factor — healthy, structurally normal birds with excellent vitality. Dun Fallow and Pale Fallow are fallow mutations affecting TYR/TRP1 pathways and show reduced eye pigment (reddish or dull eyes). Bronze Fallow (also TYR-related) carries extremely high mortality when homozygous. Olive birds have normal dark brown eyes and normal foot colour. If in doubt, look at the eyes.