there are lots of ways to do this effect. One way would be to export the video to flm format, open in photoshop and make a new layer, over that new layer paint black over the dress in all shots. Then make another layer, go back the the first layer and use the magic marqie tool and select everthing outside those black masks in 1 click. Then, paintbucket black on layer 2. After that inverse the selection and delete the first later and the video layer, now you have nothing more then a mask of everything but the dress outline. Then export the flm file back out under a different name and inport into adobe after effects overlay on top of original video and select a desaturate filter. So now everything but the dress has lost color. And then change the hue of the original file.

I know my expanation wasnt quite newbie friendly but its just one way to go about it

Or you could always just do all your coloring stuff in photoshop.But masking it will give you more control to perfect

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