Probably not a good idea to mix your whites as one always ends up looking dirty by comparison, especially if adjacent. Surfmist is a great colour for walls and large areas, but it isn't really a white when you compare it with a pure white as it has grey/blue undertones. I would suggest that you change you garage door to a mid-grey, possibly similar to shale grey, so it recedes and is less of a feature, and use your whiter-white for all of your trim and windows.

Best of luck,

Dr Retro

of Dr Retro House Calls