Actually, try it again...
Make a new instrument track, and then a new midi multi.
Cable the midi multi to the instrument track.
The Inspector should have an icon that looks like a midi cable, port will now read "Off", and channel will be set to "All".
In the environment make sure you select the entire multi, not a single channel. When instantiated, all the channels have lines through them.
First, change the name of the multi to PLAY by double clicking on the name in the inspector, it is named (Multi Instr.) by default.
Now, if you select a channel here, ANY channel. if will be shown as "PLAY 1" for channel one, PLAY 2 for channel 2 in the inspector in the environment layer. Guaranteed.
Next this: First, make sure you have the main multi midi object selected (this can be verified by having these settings shown in the inspector: Icon checked, port off, channel all, nothing else, other than the midi icon.
Put you curser on the midi cable icon, press and hold. A selection of alternate icons will show up. Select ANY one other than the one it currently has (the midi cable). A dialog box pops up and says "Change for all sub channels" and has 2 choices: No, or Change. IF you select change, any enabled midi channels will now show the icon you selected. This works the same way with colors.
One strange thing: In the environment, when you select an available midi channel, it will say "Play 1". In the environment, it will say "Channel 1". Gotta love Logic's Logic.
Just like Region VS Track based automation. Creating a fade up on a region, and then a fade out with track based automation over the exact same place = chaos
So, I hope you take the time to review what I said, especially now that I have clarified it as best as I can. Logic does work as I suggested. I would suggest it if I hadn't verified it (or in this case did a bit on it in my first VTC "Logic Platinum 6" tutorial a few years back.
I admit to being a bit snarky, but I usually only get like this when I am pretty sure I'm actually correct ;-)).
So, you learned something, and I verified exactly how it worked. We both win.