If your orchid's roots do not turn green, try soaking them until they do and then watering more often. Just a note...some orchids do not have roots that turn green (i.e. Paphs).
Most of my orchids are mounted or use lava rock as a medium so having the visible roots turn green is a good way for me to tell if the roots are getting enough water. If you are growing in a medium that decomposes, you might need to be careful.