Crystal eyes is a random mutation that affect Kiseilians' eyes, giving them colour even if the specie have only black eyes.
This mutation is really unpredictable since there's no sign that shaping up this particular mutation and every colour is possible!
Remember to follow the rules of pupils!
Eyes' colour due to this mutation it isn't inheritable, so the offspring of these subject will have only black eyes.
If offspring present this mutation, they don't necessarily have the color of the parents' eyes (so the coloring is totally free).
✓ - Any colour, saturated and desaturated (also white, as long the pupil is perfectly visible)
✓ - A visible sclera (White, Cream or Black)
X - Eyes without visible pupil
X - Coloured sclera (you can't have green eyes with red sclera)
X - Fluo/extremely saturated eyes (let's keep it as "natural" as possible)
Crystal eyes can interact with other mutations if they appear on the same Kise, here some useful infos:
On Hydra, you can give colourful eyes to one head or on both.
With Blind eyes, you can create colourful eyes with not too much saturated eyes and white pupils.
With mutations like Melanism, Leucism and Albinism overrides Crystal eyes and therefore hides it.
On Spider, both pair must have the same colour, maybe they could change a bit on shade, but if you one of them is dark green, the other one can't be lime, for example.
Crystal Eyes can only have one color. However, if Chimerism is present, it is possible for the Kise to have two different colors as long as one eye is covered by the chimeric genotype.
Same thing happen when your kises have Crystal eyes and Marble marking, allowing eyes to have two different colours.