I am making a beer pong cake.  I decided to mold RKT in shape of a cup and then I have covered them with modeling chocolate.  My question is what is the best thing I can use to resemble beer in the cups?  I am concerned jello would liquify when it got warm.  Thinking of using isomalt that I can form and then place on top.  Suggestions?

Don't use the isomalt, it will stay clear. I would use sugar because it turns the amber color.

I was planning to color the isomalt a yellow/amber color.

I'm just concerned that the isomalt will start to dissolve if left out too long due to humidity, etc.

Yes it probably would melt a bit. I did a bucket cake and used the sugar and corn syrup combo and it held up very well. It didn't melt or anything but I used a circle mold so they looked like chips and they formed together and kinda sunk into eachother.