Playstation 4 controller flashes red instead of white?

I noticed on one of my two Playstation 4 controllers that one of them flashes red when you press the PS button (not used for a while). Normally the controller flashes when you press the PS button to mean that?

Doesn't mean anything, unless you used 2 controllers at the same time (blue = 1st player and red = 2nd player) The main thing is that the controller works.