Well, it will be too much of them.
Because there are brown, red, blue, green, orange, black, yellow, amber, pink, etc common colors. So, it will be around 70 hetero-combo. :?
Is your "red&white" is possible to meet in real life?) Blue&green (green&blue) and brown&blue (blue&brown) the most common in real life, so they are realized.

You want Mint & Aqua het, but maybe someone want Sunglow & Starshine het or Fire Opal & Amethyst het. Or what about Sunset & Solidate? Cucumber & Seaform?)
It's too hard to please everyone.
And do you thought about colors that will passed by Mint & Aqua het?)
In your opinion, Mint & Aqua het must pass (green, ice(!), mint, olive, seaform(!), aqua, crystal(!), blue) eight 'fail' colors? It's TOO much for custom eye color. Only one eye color now pass eight colors and it's Dawn - and, as far as I know, they are breed-only. x-x

I can understand part about COMMON colors hetero, but hetero from SPECIAL is.. don't support due to special colors hetero, sorry. v_v