Is it possible to access the RGB values of the EV3 Light Sensor?
Green does tend to be tricky on the LEGO EV3 Color sensor. Example

Here are some suggestions:


Build a shroud to eliminate ambient light. I have seen people use electrical tape for this or build something from LEGO parts.
Using the raw RGB values, convert to HSV (there is a link in Example 1 for this).
Use the algorithm for the NXT color sensor from the EV3 source code. It will probably have to be adjusted a bit for differences in the sensors.