I have never seen an any explanation of who decided which teams wore what color kit. Wearing a color that is different than your normal kits would seem to make sense to me if you are trying to call attention to the program. If you go out wearing something very close to normal what exactly is the point of the promotion? Looking at the lists from 2018 and 2019 it looks like about half the teams switched up from dark to light or vice versa while half the teams stayed with same. Obviously the specific match-ups would have had some impact on that.
When I first turned on the TV for Revs-Red Bulls, I thought the Revs were in navy and wearing the blue shorts that they wore in the Open Cup in past years. I figured the Red Bulls had some kind of new away/3rd kit that was light blue. But it was the opposite, the Revs were in the light blue.