I have no idea if this will catch on since there's more involved than most of the threads, but it's always been one of my favorite writing exercises, so here's to hoping.
How would you describe a colour to someone who's been blind all their life? Take the colour that was offered in the last post and engage the other senses to give a blind person the clearest idea possible. For example:
Red is the passion that you can feel coursing through your veins, but it can also be complete rage that settles hot in the pit of your stomach and threatens to burst through your very skin. Red is the taste of copper or a loved-ones lips. Red is the scent of a rose wafting through the air. Red is the sound of your own pulse in your ear after a hard work-out that makes your skin warm to the touch. Love is the sound of a scream or the whispered promise of passionate night. Red is so many strong emotions bundled and twisted until you're not sure where one ends and another begins. That's what Red is to me.
Your own can be as focused or as vague as you want. Just remember to try to engage all the senses, and that anything visual is pretty useless for this.
We'll keep things simple with: Blue