Some photo effects, like desaturating a scene to black and white save for one striking object — a car, your kid's baseball cap — are actually easier to achieve with a touchscreen than a mouse. Use ColorSplash to colorize your shots selectively, painting with your finger and zooming in to stay inside the lines.
WIRED Four brushes of varying softness and transparency. Save sessions and pick up where you left off. Large Undo button.
TIRED Entire app for just one effect?