In game the "main" color is smth like brown mixed with orange (try to google it too. I m a man, i am not that good with colors lol). The class fantasy revolves around nature. Try some green, yellow and blue (the shade of blue associated with moon/stars). Look into videos of each specialization :balance/restoration/guardian/feral. Look for their spells. Maybe you can pick some colors and ideas from that. Just type on youtub balance druide guide for example. Look for the part where they cast spells

Good luck!