That's really awesome. For colors, sometimes I'll see a pinpoint of colored light (like a camera flash). Everyone appears to be different, so... at least to me, the colors mean (symbolically) what type of block has been cleared from the 'chakras'. I don't get blue in the kidney area, a blue "soul-spark" (mini-camera-like flash of light) for me means throat center has something that opened. Sometimes I'll get red from my head (probably too much thinking of the sexual energy >_< ) when it's released, but other times indigo (like the color is for the upper head centers)--other times I'll even get a light that's crystal clear like water (the best feeling EVER)
However, (I'm just taking a wild "guess") in your instance, the blue 'kidney energy' could be some kind of energy that was meant to be in the kidneys, and by practicing you've released the 'kidney energy' that may have been stuck in another area of your body--say the chest...and your just sending it back to where it belongs. Like I said, wild guess. I have no idea what the 'colors mean for you' that's something that you and your soul have to work out. (or I'm totally off and one of the Masters around here will enlighten you further...)
God bless,
~Z
