Display Calibration

Yes lol.. Your external display, might have a different DPI ratio, and different colour settings. (alpha etc)

there is a display calibration tool in OSX under displays if your interested

PTP

 

No, I don't think you do. You just do it once for each, because when i have my macbook connected to an external, it has a different wallpaper. I don't really know if that's relevant or not. I just said that because I always figured that meant the macbook saw it as a display with different settings. And yes, it is when the clamshell is closed. But, this reply could make no sense and I just sound like a dumbass, haha.

 

you should have a calibrated profile for each display you use. usually once you set up a profile to a monitor, the MBP will automatically use that profile for that monitor every time you hook up to it. you do NOT need to re-calibrate every time you connect them.

having said that you should re-calibrate every monitor and laptop every month or so