I just followed the last poster's suggestion. I went to the RFS6000, and swapped the wires of one of the "red" AP's and one of the "black" AP's. That is, I disconnected the "red" AP's wire from the ge4 port and the "black" AP's wire from the ge3 port, then I reconnected each of them in the other one's previous port. When the AP's went back online, I checked them out by accessing the RFS. And lo and behold, in spite of the port switch, the "red" AP had stayed "red" and the "black" AP had stayed "black".
Now, I have returned the AP wires to their original positions, and predictably, the AP's remained colored in the same way as before.
That is, whatever that color signal means, it isn't about the ports on the switch. It's either something to do with the AP's or with the wires they are connected to.
I reckon my next test will consist of disconnecting one of the "red" AP's and connecting it to an available Ethernet socket in my office, letting the RFS detect it through the corporate LAN and seeing if it still appears "red" (to rule out some issue with the UTP wire).
Thanks for the good advice!