Well, I will give him the benefit of the doubt and assume he said pink is okay for China because he's used to it from Civ4 vanilla, and then tried to rationalize it.
Personally, I pay more attention to choosing the "right" color for every civ than what would be entirely justified, because I think it's part of the right feeling. Khmer and Mughals should be some shade of green in my opinion (for whatever subjective reason), and Holy Rome and Spain should be some sort of yellow. Poland is associated with red, but with two dark red civs nearby (Russia and Italy), and red England isn't that far off either. So the only shade of red that doesn't verge towards pink would've been a faint red similar to Korea's, and I don't think that would've looked more fitting for Poland.
So I chose the current color. It's called amaranth in the game files by the way. So it is not pink. And similar shades of colors are often used for Poland/Lithuania. Paradox games have been mentioned already.
I don't really care which cliches are associated with colors. I mean, we're all playing a game full of a rainbow of colors, so we're gay anyway
For the Vikings, I don't have any strong color association with them. I didn't have one for the Tamils either, but I knew they couldn't use shades of purple to get more contrast with India. The Vikings originally had light purple in BtS so I thought it wouldn't hurt to switch them around. It's not that noticeable next to the other European colors in my opinion anyway.
So you see, I did put some thought into the civ colors. Actually whenever I consider to add a new civ, I have to think for a long time how to give them a suitable color that isn't used by someone else already.
For that post, I love you man.