It's been sitting in the fridge since last night so it's good and hard. Can I re-melt it and add color to it? Or do I have to knead it in as if it were fondant?
(slapping forehead)

I don't put mine in the fridge, so I don't have trouble kneading it back up, but I just add it after, using gels. I sometimes add a little fondant as well.

Yes I use gels also. It's about room temperature now so I will add color to it.
Every recipe I've seen says to let it set up in the fridge for a few hours. I thought you "had" to.
And may I ask why you add fondant to it?
Thanks for your reply!

You can add gel coloring to it, but it's going to react just like melted candy melts, meaning it may try to seize up on you. Just add a little shortening to keep it smooth. I never refrigerate my modeling chocolate. Treat it just like you do fondant. I use a 50/50 fondant & modeling chocolate mix when I need something to hold its shape.

You are right, I don't know why I would add gel color. I have candy color. Thanks for the tip on adding fondant and for all your help to both of you!

I color my modeling chocolate with regular food coloring after it's made and never have any problems...it never seizes up .( I have candy color too but not a huge variety.)
I don't refrigerate it either, I've never seen a recipe that says to do so....so I didn't

I do as Jason-Lisa. Never a problem. I color each log of modeling chocolate with americolor gel. Then i have whatever color i need for what i am making.

Liquid food colors work fine. Modeling chocolate cannot seize once it's set. You can knead the coloring right in. Add some corn starch along with if adding a lot of color.

Refered to your book on modeling choc.  Took the red, yellow, orange mc and followed your directions on adding more color with corn starch.  What a difference.  It worked perfectly.

I also read your instructions about adding color when you're making the mc.  Thanks.