The middle of these shapes look like they're tinted by the light orange outlines, but it's an illusion.
Known as a "watercolor illusion," this effect occurs when a white area is surrounded by a thin, brightly-colored line which is itself surrounded by a thin, darker border.
The illusion was independently discovered by Italian psychologist Baingio Pinna in 1987 and by Jack Broerse and Robert P. O'Shea in 1995.
Scientific American breaks down the science behind this phenomenon here.