IMHO the best way would be to have only red and green as AP colors, even if they not count and raises or lower the AP level. This way there would not be any "grey" confusion, and the most important thing for me is to see if people likes my posts and threads not the value of them, since that system easily can be abused.

If one senior with lots of AP's assigns me positive AP's for a thread many people may think that he shall not have more greenies. If the AP's was worth less more people would assign AP's (and make comments) to different threads and posts. Most important for me is feedback and I guess many other think like me aswell, this is only a idea and I may be wrong .