as a further note you have to remember that boric acid will only dissolve in a solvent that is POLAR!!
your petroleum distillates are not polar so your boric acid wont mix, at all, it will coagulate down at the bottem and not even effect your burn, the sodium content is also very high in petrol, because it burns hotter its what they put into fuels to get better effeciancy, this is why you should use aviation grade kero, or ultra pure lamp oil (next best thing)
and if your going to do extensive colours, have a different pair of wicks for each colour, and label your wicks so you dont contaminate your chemicals
all you need is a little bit of sodium, and your darker reds and purples just wont show up, the sodium will completely overpower the hue that you are trying to acheive
keep it coming people, this is becoming an definitive thread