In my opinion, black is the easiest colour to describe to a blind person. Ask the person what they see? When they answer nothing, that is the colour of black. Dark, unseeable. Or at least that is how I would describe it.
Opinion
I would describe it as dark and mood setting. It can also mean some one or thing is in a bad mood.
Instead of just thinking of it as a color, try maybe a feeling or a place or night time in...
You can describe purple by putting their hand or something on cold metal. =]i did this to my grandpa who turned blind at the age of 13. being in darkness so long, he forgot colors so he asked me to...
I think it is nearly impossible to describe any color to a blind person, unless they weren't born blind. They might understand the color black because that is all they see.