There is no set way to do this, although the colors are somewhat consistent - white for beginners chip, etc. I have beento a meeting where they give chips away for every month up to a year, then yearly thereafter.
Also, all the meetings around here they give chips away at EVERY meeting.
I have been to groups in different parts of the country that NEVER give chips away. This was a part of AA (I am told) that Dr Bob and Bill W were not in agreement with.