I wonder if this could be used to prove prior art in cases that involve certain colour combinations.

As I understand it colors themselves cannot be trademarked. The trademarking comes in with the combination of color and product type. So Lyft and T-Mobile can both be electric pink, but Uber couldn’t rebrand to be electric pink.

Cadbury had their purple colour trademarked for awhile https://www.thedrum.com/news/2019/02/05/after-two-decades-ca...