I've been seeing these videos in my recommended basically they have this image and they color in different parts of the body which are all in the colors which are on the side of the image what do these video even mean? why are they all colored in different colors?

I've been seeing these videos in my recommended basically they have this image and they color in different parts of the body which are all in the colors which are on the side of the image what do these video even mean? why are they all colored in different colors?