Another Mystery.....

Trying to make vivd saturated or colors that 'pop'...how do they do it ???

I'd tried it on a couple of pictures of my nieces I got today.
The one with the yellow, seemed to have spilled over too much on her face.
When I tried to mask it out, it leaves this black that I can still see???

Anyways, the girls get to enjoy the hot tub....not so sure the adult are getting much time in.