Its all about money/effort. Sometimes you get a guy turned green with just an AC scout, and if no one else goes after him, he will stay green and you can sign him. If another guy goes after him, it will be easy to "flip him" to yellow, or even red on just one recruiting cycle. In other cases, you my have a guy who is green and you have put a LOT of effort into him....but another coach is doing the same thing. It will be harder to turn this recruit, but can be done.
So...you have to "guess" a little bit and try to outfox your recruiting opponents. If its a guy you really want, and you got him green on the cheap...you may want to "add a little insurance", in order to avoid the scenario in which another coach spends only a few dollars just to see what happens...and he turns yellow. Then that coach knows he does not have a big battle on his hands and might throw more money out there.
ABOVE ALL: do not spend all your money before the signing cycles.....you need to keep "some" in reserve.
Hope that helps.