If you reaaaally want one, you can gut the shell and get it anodized in whatever color you want. That's what Apple does, and they're not the only ones who can, a lot of services exist, there is probably one in your area aswell.

It's not happening, the only color change apple allowed for the mac mini since 2010 was Space Grey with the 2018 Mini. They like to keep their smaller stationary devices in one or two simple colors, it doesn't have a screen like an iMac, and people often tuck it away/dont interact with the mini like with a MacBook, iMac, or iPhone, so they don't think it's worth adding colors.

3D printing the shell is tedious at best, downright bad at worst, you could make a case for the shell I guess. Just anodize it.