The energy of the photons (bits of light) is determined by their frequency.
E = hf.
Where E is the energy of the photon, f is its frequency in Hz, and h is Planck's constant, h = 6.663*10^-34 Js.
The results you get will depend on what you use as your light source, and what kind of filters you use.
The visible light spectrum spectrum runs from approx 450*10^12 Hz (red) through to 750*10^12 Hz (blue). So red photons have the least energy, and blue photons have the most energy. Green is in between the two at about 600*10^12 Hz.
So, when you have no filter, all the photons can hit the solar cell, and you get the best efficiency.
Given that the red filter is giving you the next best results, I'm guessing that you're using what are called notch-filters. These are filters that only block a particular colour. So when you use the red filter, you're losing only the low energy red photons, but still keeping the medium energy green, and the high energy blue photons.
When you use the green filter, you're keeping the low energy red photons, and the high energy blue photons. When you use the blue filter, you're losing the high energy blue photons.