I had no problems with the RGB Led supplied in the kit, however when I tried to use another RGB Led I had a similar problem with the Red light drowning out the others. After consulting several sources here's what came about,
LED's from the same manufacturer but in different batches can have varying visual results, once you have assured all your pins are connected properly you can either tweak your code to use PWM to equalize the light levels(this can get a little messy one the code end) or experiment with different resistors on the pins.
To solve my issue I first place ad 220ohm resitor on the red channel, this brought the red level to not drown the others out nut made the green drown out the blue. I then placed 220ohm resistor on the green channel, this effectivly balance the three channels in my RGB LED so I could produce white light.
The same resistor value may not work for you but experimenting will find the ones that will . If your green is not lighting up enough to be noticed start with adding a 220ohm resistor to the red and blue legs.
Also keep in mind that in this project the light of the room your in is filtered through the colored gels so the type of lighting in the room can effect the outcome. I have florescent light and got much more noticeable results with the color gels removed.
Lastly you could use a calibration routine and some funny math to first set and balance readings from the photoresistors.