Thank you all who posted suggestions and issues here. We have begun discussion how we can make our games more accessible for people who are colour-blind, and I think we'll manage to cook something up for CKII. You writing about it here really helped to lift the issue.
This is what I love about Paradox, the paradox-people actually listen to you and read what people are writing and want. Good work Paradox, hopefully this will help some people