This is my thinking on Red. Once a players attribute hits RED, I put it at zero. My thinking is, if he does lose a couple of points (rare), it will go back to yellow and I'll know there's some points to gain.
Leaving 8 points on them just to avoid losing a couple of points seems like a waste. There are better use of those 8 points on green, black, or blue categories. At least until their senior year and most/all categories are maxed out and red. Then you can leave the 8 points.
Matter of fact, I like seeing one or two non-core values being red when recruiting. I then know I can max out their core values quicker. Like seeing Blocking red for guards.