About ten years ago, compilerbitch posted a photo she had taken of doseybat leaning on a balcony and looking out over... a seascape, I think. It was black-and-white and had a grim look to it. Then I happened to see the colour original, and was astonished at the psychological effect the blue sky in it had on the feeling of the photo.
That gave rise to an Idea (which, like all of my best ideas, sat around in the back of my mind for years before becoming reality), of making a similar photo, in which like clouds drifting past, patches would drift across the photo, only these would be patches of full colour on a greyscale background; and then eventually one would come that was large enough to encapsulate most of the photo and bring life to it before departing again.
Doing this idea proper justice, i.e. at a high enough frame rate to look smooth, would involve convolution matrices and be at the limit of my technical ability. It would also involve more time than I am going to have this side of my wedding; so here, to give you a taster for what it would be (and probably scratch my itch enough that the full thing never happens now) is the work of most of an evening instead: