Candles are just a focusing tool. They aren't needed, but many find them helpful. I know I do. However, green isn't the only color associated with money. Gold/yellow can be due to the link to Gold as money. Silver can be used the same way. However, white is the all purpose color to turn to when you can't get what you want for a spell.
I really suggest you look into common correspondences to colors. This will help you with any spell work you ever attempt. After you learn the basic properties of each color, write out your own list. For example, if you lived in a country where the paper money is another color than green, that color would most likely represent prosperity to you instead. Point is, what you associate with a color is very important and should be considered when you work on correspondences.