This Product Ideas board is currently undergoing updates, but please continue to submit your ideas.
Personally, I like the default color options (despite the limited number) that are provided for the base/interface appearance color. That said, members on my team really wish we could match the exact color of our base with the primary company brand color. I feel like it wouldn't be too hard to have an 'advance' section under appearance that allowed us to input a HEX number.