Eye colour is genetically complex. It is influenced by multiple genes acting together, not a single gene with a simple dominant/recessive pattern.
Eye colour used to be taught as a simple trait where brown was dominant over blue, following a basic school-textbook inheritance chart. That model is now known to be incomplete — eye colour is polygenic (influenced by multiple genes acting together), so a simple one-gene dominant/recessive chart cannot reliably predict a child's eye colour.
A region on chromosome 15 containing two genes, OCA2 and HERC2, is the largest single known contributor — variation near HERC2 controls how much of the OCA2gene’s protein is made, which in turn affects how much melanin ends up in the iris.
Researchers have identified at least eight additional genes beyond OCA2 and HERC2 that play smaller supporting roles in eye colour — the two named genes are the largest single contributors, not the whole picture.
Parents' eye colours affect the range of likely outcomes for a child, but do not guarantee one. Two blue-eyed parents most often — but not always — have blue-eyed children; genetic variation can produce unexpected results, including brown-eyed children of blue-eyed parents.
Colourwise does not offer a baby eye-colour predictor or calculator. Given how many genes are involved and how much individual variation exists, a genuinely reliable predictor would need clinical-grade genetic data, not a simple parent-colour input — building one is tracked as a future evidence-and-ethics review item, not assumed to be a safe default feature.
Eye colour reflects an individual's specific genetic inheritance, not their ancestry or ethnicity as a whole. Colourwise does not use eye colour to make or imply claims about someone's ancestry, ethnicity or identity.
Source: MedlinePlus Genetics (U.S. National Library of Medicine). See how eye colour works for the underlying biology.