I recall uranium being added automatically to the ore registry and the sieve registry, is this not the case anymore? or am I just misremembering?

It might've on an previous mod, Creatio is not set up to do that. It does yellorium with a uranium oredict if big reactors is installed.

If you have a color suggestion I could add uranium to the defaults or add an IE/IC2 compat class.

I had added the colour as 4e5b43 ;
it seems close ish enough to Immersive engineering's

but then I messed up the fluidblock transform registry and the sieve registry and disabled it again because I didnt feel like troubleshooting my jsons I just wanted to plug and play (though that's just delaying the inevitable because I will have to add stuff because I want to add ways of getting astral sorcery to my skyblock)

if you take the time to add it to the defaults I would be very thankful!

the chunk drops for uranium should probably be rarer or as rare as the gem drops I reckon