Me too!! Only found out when doing titrations at school in preparation for my GCE's. My results were all over the place. I was told at the time that 9 out of 10 blokes are colour blind 'to some extent'. Most, so slightly, you never know (unless you have very honest friends).
That was one of the reasons I never really got into colour printing. I did transparencies in the main, and my beloved black and white. I have problems when colours get very dark or very pale. consequently, subtle hue corrections are a bit hit and miss. I'm far more adventuous with colour now with a digital darkroom that costs nothing to get it wrong. In the past, the sheer expense of the materials, equipment and chemicals made failures painful in the wallet department.
Interesting what Dave said about composition, because I find myself far more aware of composition rather than 'the too warm tone caused by incorrect white balance settings'. Having said that, I'm no expert, and have absolutely no qualifications that makes my comments any more valid that anyone elses. When I look back, most of my important photos seem to have captured the moment well. I don't do much cropping unless I want to have a new take on an image. As an example - this is straight out of the camera - no cropping or any other work:
Maybe because I know that my colour perception is suspect, I do subconsiously concentrate on composition. I'm not suggesting that my pics are all superb compositions, just that i'm perhaps more aware and by the law of averages, some are OK.