Custom Slime Block

Hello everyone. Looking for some help if possible. I'm trying to make a mod that contains many different types of slimes. This results in the need for multiple different colors of slime blocks. Unfortunately I've not been able to get any option I've come across to work.

I've already tried HERE / HERE / HERE and HERE

None of that worked. I'm using MC 2023.1

I'm sure it's something simple I'm not seeing. But any help would be great.