Greg Cox wrote:
And, bizarrely, War of the Colossal Beast (the sequel to The Amazing Colossal Man) is b/w until the final minutes of the movie--when it inexplicably turns into color.
Not quite inexplicable as it was done quite literally for the "shock value". After the sister of the titular character convinces him to gently lower a bus of school kids he was going to crush, the Colossal Beast has one last flash of humanity that leads him to conclude it would be better for everyone if he were to 'end it all". Thus he seizes the power lines draping from a tower. The second he does this and the sparks fly, the film switches to color, thus enhancing the sequence.
(IFC recently aired it, so that's why I remember it.)