Recently we captured the first image of a black hole, and for some reason, the first thing I thought of was Celestial Vortex.
Instead of Celestial Vortex copying the blue colour from Electron Vortex during its suction, why not use the orange colour from the image of the black hole?
It'd be a nice way to add something unique and noticeable to the bomb, and would be a neat reference as well.
Orange also complements fire well, just like blue matches with shock.
This would be a neat twist. It would also make it easier to tell what bomb is being planted if you aren't paying attention to the user dropping the bomb.