How to make a soft multi color overlay in Photoshop

I believe a gradation was created and used in the cigarette.

For the frace, the gradation area was enlarged and a Gaussian Blur was added.

Then the area was shaped and locally added to with a soft edged brush (which I did not do. Another option for shaping would be to use a large area soft brush applied with the Liquify Forward Warp tool.)

For the cigarette a simple Gradient Layer with the appropriate Layer Mask may suffice, the hair may have been edited with Curves, the face seems to have been painted over, possibly with several Clipping Masked Layers, though for some aspects a Gradient Map Adjustment Layer may work, too.

On a new layer, select - with the lasso tool - the area that you want to recolor. Then select your colors on picker  - foreground, and background - two you want to blend,  Now drop color into the selected areas by drawing a line using the Gradient tool and place the blend of colors into the selected space. You can also then choose to decrease the saturation of color using that layers slider % to make it more or less color. Lots of experimentation is required. Fun! JH

Stack some Render > Clouds layers, and experiment with colours and layer blend modes.

You'r best bet would be to use a blending mode to get it to lay on there. There are more ways as well, like displacement mapping, but that's getting way more involved than what would be possible to explain on here.