It depends on the brand. I use Wella which is a demi color. You can use either with heat if its been a few weeks after your last relaxer OR, without heat if you're relaxing on the same day.
I use a dark brown instead of black because of my coloring.
Rinses are by nature semi colorants because they don't penetrate, they just coat the strands. Its the same with Demi colors as well.
You'll have to be sure to use a good moisterizing conditioner after so you're hair isn't as dry.
-A