As the bolt is shagged and not going back in the colour kit, is there not enough room to try and use a pair of pliers to hold and turn the bolt ??? as this was only tightened originally with an allen key this should be simple enough to do.
Or a cold chisel into it and then unscrew it as wiggles said.
I agree. Brute strength and a pair of pliers would take the screw off. New colour kits down use that type of screw, they use a philips screw and screw it directly into the plastic. I know because one of screws wont tighten, just spins around
if you are really stuck i have a spare colour top, its got a broken lid so you'd need to swap your lid in. either way if your stuck and need to resort to just breaking it off i can send you a replacement for a few quid.