Assign repeating #s to posts.

I want to assign 1 of 10 (repeating) custom colours to posts. So I think I need to first assign a number, 1 through 10, to each post, then assign a colour to each number.

In the loop, it’s as simple as a counter to assign those numbers. But I want the colour to carry over to the single post template. So if it’s blue on the homepage, it’d stay blue when you click the blog post.

Make sense? I don’t even know where to start with this one (even though I create custom wordpress themes).