I would think that it would dry unless you had a lot of moisture in there and if that was the case I think from what I have read and heard tonight that your stuff might be messed up if that was the case. Are you just planning on painting with the straight gel color? I don't see why it wouldn't.
I know you already tried it, but if you mix in a little white powder color, it makes it more of a paste and it dries easier. Maybe next time 
I've painted with gel colors mixed with lemon extract on gum paste/fondant mixed shoes, numbers and other things. It will dry overnight as long as there isn't a lot of humidity. I have not paint my gum paste/fondant pieces with straight gel paint. I would like to know how that dries. I have read in other forums to use either lemon extract, vodka, or everclear. I haven't gotten my nerves up to buying alcohol yet(LOL). At my age, I won't get carded, so it is just me being old and nervous. 
Quote by @%username% on %date%
%body%