My DCs school uses this system. Up until this year it was just flash cards but now they have charts on the wall with every childs photo, if they manage to stay in green for a period of time they get a reward.
I have a child with SN (ASD) who is regularly in and out of amber and the occasional red and I have found since this new less discreet system has been introduced it seems to have made his behaviour more of an issue amongst his peers and other parents (evidence is on the wall for everyone to see).
Whilst I'm not suggesting my DC should be allowed to do as he pleases, the old system worked well and didn't make a massive deal out of it.
IMO children will do well and behave well if they are able, if they don't it is usually because of a barrier- special needs, family problems etc... for a lot of the children staying on green will be as natural as breathing. For the most part it will be the same kids negatively highlighted for their behaviour week after week.
I doubt my DC will ever be able to sustain appropriate behaviour for long enough to be rewarded in fact his behaviour seems to be worse since they introduced this.
I feel that for some kids using this as a one size fits all approach is probably a breach of the DDA.
I am interested in opinions as I am going to discuss this with the senco at our next meeting.