Here is the full list of all 17 Rainbow Reactor achievements.
Reach Max Multiplier
Complete the 1st shift
Complete the 2nd shift
Make a Quadruple Reaction
Make a Quintuple Reaction
Complete the 3rd shift
Complete the 4th shift
Complete the 5th shift
Complete the 6th shift
Complete the 7th shift
Complete the 8th shift
Complete the 9th shift
Make a Sextuple Reaction
Make a Septuple Reaction
Score Over 9000
Mix a brown C-Ball
Get the highest Reward at the end of a shift