It seems that you cannot do much to change the region colors, but you can change the BaseHue values of the 24 (x 3) regions of the color picker (the “Colors” palette).
After making a back-up, open the mapping.plist and navigate to Colors > Regions. You will see 24 items.
Then open this LPX template with 24 x 3 regions, each colored accordingly to the region in the color picker. You can use it as a tool in tuning your palette – to see better what the colors really look like. Each bar (1, 2, 3…) corresponds to the item (01, 02, 03…) in Color > Regions.
As the colors are always set-up accordingly to the values that were saved in the mapping.plist while you started Logic, you have to hit save in Xcode and to restart Logic to see what the new values you typed look like.
For an example of the results, well you see it above and below. Here I have returned the reds Apple took away in LPX. For I do like red especially as a sign marking my output and group bus channels. Moreover, as I don’t really like nor need all that purple Apple gave us, there is far less purple in here. But I do like orange, haha, so there is now many tones of orange. – If you like that, you can obviously skip using the template tool and just use Xcode to type the values in the screenshots below.
(ps. An easy way to go back to the default color picker later, at any given moment: open your back- up of Apple default resources > MA…mapping.plist, navigate to Colors > Regions, copy that file by right clicking, open your own MA…mapping.plist file, paste it to “Colors”. It will show up as “Regions – 2” but delete your own “Regions” and the “- 2” in the name of the former.)