Hmmm...what about bloodshot eyes? Could that be considered canon, assuming we can find a shot or two, or would that be another one of those "not sure whether it's canon or makeup" situations?
Edit: The thing is that unless the shot is under fairly bright light conditions, I don't know if even bright red blood pn Cardassian skin would show up as right red. Colors are tricky. Not even human blood always looks bright red.
Hmmm, if we're taking about bloodshot eyes the only time we get to see them is when Damar is in his alcoholic phase but the lighting is always too dark to see.
I hate to say it but we might be stumped on this one...