Does it make a difference when you unplug the Crumble’s USB connection?
There are a couple of possible things happening here:
1) It could be that the batteries are nearly flat – the Red part of the RGB LED requires less power so when the batteries start to die, only the red may shine.
2) If you have a loose connection in one of your croc-leads this could result in a signalling issue so it is worth double checking each one work properly.
3)Another thing that can yield unusual results is if you connect the Sparkles back to front – make sure the arrow and D point to the right.
If you continue to have any problems, please upload some clear photographs of your setup.