Happs comes in arcade optic boards (old "green" vs new "red"), and PC optic boards (ps2/USB ready).
The red vs green is arcade only, and only apply to the TBs you need optipac, optiwiz, or mouse hack to work on a PC. IME, there is very little noticeable difference between the two, even though happs claims the reds are better.

(I have both.)
The PC ps2/USB boards, OTOH, have had a couple versions that AFAIK are not noted by color. The old PC boards, if you've been read here for a while, seem to have a fairly high failure rate. (This is compared to all other TB boards; the total rate
might still be low like 1% of all old versions failed, but people have been posting these board far more than any other board here.) Some of the failures occurred after a period of time of working fine, others were bad from the start. Happs now has a version 2 of these PC boards, and people haven't posts failures of this yet.
The way to tell the difference is the new PC boards say "ver. 2" and the old ones don't; there is no color difference. (Can someone verify this? I only have the arcade boards.)
I think the confusion is between the arcade boards and the PC boards, and the different versions of each. Basically, don't get the old PC boards, which can be hard to tell since they don't have a different color or say "These board suck!" on them.
