Upload & Sell: Off
This is something I have not tired. Interesting shot.
This has to be about 1tbsp oil and 1/4tsp food coloruing: Say 1/16th tsp blue. 1/16th tsp red, 1/16th tsp yellow and 1/16th tsp red...Here is a quick shitty set-up with 1 speedlight (F/22 (1/64th power) shot at 1:1 with a sheet of baking paper directly below.
This image is terrbile I know, but is just supposed to give you an idea!:
Here is how I did it: (I'm still learning)