FW 5.12 - What do the different colors mean in WLT?

I notied on FW 5.12 when doing a MU-MIMO link test on my 4600 AP that the MAC addresses for the second SM are listed in 2 different colors. One green and the other a teal blue. What do those colors mean?

Subscriber Modules (SMs) that are capable of forming an MU-MIMO group with the primary SM are highlighted in green in the Wireless Link Test selection list.

What about the teal colored ones? I selected a teal colored one for my second SM and the AP did mu mimo between the two for the wireless link test so why are some teal and why are some green?

Teal vs Green must mean something different since I have 17 SMs on this AP but the MU WLT SM list only lists 11 SMs for a total of 12 including the Primary SM. SMs that cannot group are not listed in the drop down.