Rainboduino temp monitor?

What I would like to do is make a rainboduino change colors as a temp probe changes temp. With an rgb matrix plugged in, is there any input pins left to attach a probe? Would I have to use an arduino to control the rainboduino thru the serial connection and if so is that difficult? My programming skills are a little rusty, but i think with a push in the right direction I could figure it out.

Thanks