BrickColors in this list that are stricken through will display just fine in studio, and will change to a closely-matching non-restricted BrickColor in online mode. But this doesn’t apply to unions.
Here’s a picture in online mode. This is a stack that has most (if not all) of the restricted BrickColors. The only difference is that the stack on the left is one big union, and the stack on the right is just a stack of plain old parts.
Although I love this, I figured I should report it before trying to spread the word in case there’s some sort of behind-the-scenes consequences when using restricted BrickColors.
EDIT: Going to tack on one more minor thing I just found: In union error -7 (maybe all of them? I can only trigger -7 right now) “offsetting” is typo’d as “offseting”.