In a nutshell, you can use decimals and values larger than 4 to set your eye genetics.
I haven't tested it with anything higher (more recessive) than 5, or decimals out more than 2 places, but even if I inadvertently worked within game constraints, that's at least 600 different genetic values to play with.
I'm not sure if this is useful for anything other than getting one's OCD on, or perhaps creating dominant-recessive ranges for different species? Anyway.
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