The green could be either algae growth on the surface but it is also possible that the roots have developed chlorophyll. Many epiphytic plants that tend to have exposed roots will have chlorophyll present in those roots. Some orchids are even leafless and do almost all photosynthesis through the root system.

Mike

Good advice Mike. I only know that the completely clear containers I have hoyas in display the green roots and thought it was due to higher light. All of them are growing with no problems or deformity. ~ Mary