Well, if you want to believe that this nonsense works, which it doesn't, white candles are good for any ritual, including money. For money and riches green or gold is used, green usually, the colour of increase, just paint them, an oil based paint is best, or use a spirit (no pun intended) based felt tip marker pen, carve 'green' on to the candle with a sharp point, it is only focusing your mind to achieve the desired result, it all comes from you.
I think MickS has got it spot on. But what matters is you believe in the ritual and spell. If you dont then the colour of the candle wont matter. if you do believe in it, the colour wont matter as much