Touch screens have their uses, but until one comes out that covers the entire surface of the arranger, imagine if you had an arranger where EVERY control was crammed into a four inch area in the middle of the keyboard... That would be awkward, to say the least!
IMO, physical buttons on the left and the right give you things to hit that are close to where your hands already are, sliders in the middle give you ease of adjustment no matter WHAT hand you have free at the time, and a touch screen gives you access to FAR more parameters for editing than a simple button matrix can ever give you...
Sounds sort of familiar, doesn't it..?!
BTW, NONE of my main arranger control buttons have any color whatsoever. Just LED's to light the way. To my mind, it's more about SIZE and logical layout than color. If your key colors were reversed (Farfisa, anyone?!) would it make the keyboard harder to play?
The most important feature of buttons is a logical layout, so you don't end up with buttons better hit by the RH stuck on the left (and vice versa), and not cramming them in too tight, and ending up with inadvertent wrong button pushes, because you can't easily hit them quickly, accurately.