I fully agree with Sue about the traditional symbolism of green candles... I'd like to throw my two cents on the matter.
The colors are merely of symbolic value, nothing which is more important and deeper than this, obviously not something that will damage you for not doing it as an optional thing. Candles are used for stimulating emotion and inspiring one to feel what they are casting.
Some people don't even use colored candles, some carve sigils into them and that works for them just fine (I use this for my own spells and my own rituals as well).
The thing I recommend you personally is to go with what you feel necessary and what you're most comfortable with for your own spells, and rituals... Candle magic or using candles in magic is not an inflexible or rough practice, so if the white candles with colored coating works for you then they will obviously work for the circle casting. If you prefer solid colors then by all means, use the solid the ones instead. As I say, just do what you will.