I'm really interested in genes that could make not-cats more like my current and past real cats, but also anything that can make them more varied as individuals. Countershading, as mentioned before by owners of tabbies in the thread, is a big one that I support massively, but there's a few other things on my mind.
The first thing is saturation. Calico and Ginger not-cats aren't very bright, so I can't really get them to resemble cats i've had. Upcoming alchemy colors also don't really solve this issue, as while their dilute variants are pretty bright, and in places surprisingly saturated, they don't really scratch the "orange cat" itch.
So my suggestion is a saturation gene for not cats, which hypothetically could work like the solid gene.
Hypothetically:
DD (desaturated desaturated): All current cats
CD: (colorful desaturated): Also resembling current cats, but carrying a gene for higher saturation
CC: (colorful colorful) More saturated cat coats
While this is mostly just a thought to make non-dilute ginger tones that match real cats more, I also think this could be used to give higher variety to the browns and grays, and give a bit of a blue-gray option to grays specifically.
A mock up of saturated colors ^
Just to help illustrate what I mean.
The dilute gingers are specifically skewed to avoid stepping on the toes of the yellows in alchemy, and the black might be a bit too dark. I also tried to make nothing here more saturated than the brightest colors proposed for alchemy.
Hopefully these aren't too bright for existing sepia site aesthetic-- but with the eventual introduction of alchemy (which seems to include vaguely saturated pink and blue colors) and custom content, and seemingly no rules about the saturation level of said custom content, I feel like they wouldn't stand out too much a couple years down the line.
I also think that this could work really well as a gene that comes from "Tigerlily Meadow" on the world map, which mentions in it's description that flowers cause the area to brust with color all year round. Could they, possiblyyy, make the not cats burst with color as well?
My second thought: Dark stripes and Black stripes.
The brown tabbies would much more greatly resemble my real cats if I could have them with black, or simply darker stripes. Additionally, black stripes could create "Tigers" on ginger not cats, and "Silver" coloration on the gray and lighter dilute not-cats. I feel like this one could also just, possibly, go in the same gene slot as solid. As making stripes black would make it so that all the "solid" cats of that variety are largely the same color.
Additionally, an "inbetween" state or a version where the cats simply have darker colors would also just be nice.
Hypothetically, again:
LL: (light light) current not cats
LD: (light dark) either a carrier for dark stripes or possibly a version that simply has *darker* stripes
DD: (dark dark) black stripes
Mock-up of black stripes applied to not-cats ^
Mockup of "inbetween" stripes applied to not-cats ^
EDIT: potential issue:
Colorpoints specifically. While I can see this working fine on Minks and other point cats, Colorpoints present a situation where the "solid" color is used for the point coloration. So colorpoints would probably either need to do something strange, have unique colors applied to them, or draw from the base color instead of the stripe color as they do normally... Or just all resemble black colorpoints, but that seems like a solution that would cause confusion.
And my third thing is: Null white type.
This would be a gene that changes the white on cats to the same color as base Null. I've seen in the info section that black versions of the white types are planned, which is great, but I wish for something in the cream variety-- partially as an alternative to the lack of countershading, but also just because cream colors are cute.
^ a mock up where null replaces white on a cat
Possible issues with this:
It's nearly, but not entirely, invisible on solid null cats
It can be used to cover parts of tabby patterns on patterned null cats, creating interesting, very light, and unintended results. Same with watercolor cats.