The best food to color it up. Feed it with prawn that still have the shell on. The shell of the prawn makes contain more carotene than the meat itself. I actually just remove the horn and the little pointy thing at the end of the tail just to be on the safer side.
For a 2" jardini feed it with krills. I would recommend feeding it with varied diet such as hokari floating stick, cut prawn or shrimps, mealworms/superworms that been feed with carrots so the aros would get also absorb the carotene that the worm ate.