After looking at these from every angle (including, it feels like, upside down), I'm going to surrender and call it a tie for first place between these two:
deepop's "Gallery window" Like an Edward Hopper painting in its simplicity, muted colors, and sense of quiet that is not quite peaceful. The rectanglular lines, the off-center placement of the window, the angular light across the bottom, the reversed letters of the sign, the scene outside the window -- all work together beautifully.
zenjenny's "old picture" Muted colors with that lovely blue, simple flowing figures, again a sense of quiet that's not the same as peaceful, beautifully balanced, and the dark layered in between the figures and the bright light behind them like a barrier, as if expelled from some sort of Eden. (I should also add: Provokes flights of fancy.)
And because
zenjenny was judge just a week ago, I'm going to pass the baton, er, staff of office to
deepop to be judge for the next MobiColour.
Honorable mentions
lkbside's "Laser harp" (I hope you all realize this thing is an actual playable instrument!),
Mo-Co's "Light and dark sunrise" (golden color and those sharp little birds on top of almost every pier), and
zenjenny's "Making moons" (if a Wyrd Sister were making a moon with her hench-bats to help, it would look just like this).