I messed around with this some more, and I found the tween behavior actually has a color property you can use. So this can be done with just one event and no additional variables.
+ System: Every 2 seconds
-> Sprite: Tween "" property Color to rgbEx(floor(random(101)),floor(random(101)),floor(random(101))) in 2 seconds (Default, destroy: No, loop: No, ping pong: No)
I also updated the example file with it in the Layout 3.