My favorite way to tackle this problem, assuming you have both of the two colors on separate layers is a combination of the previous two mentioned methods as well as using a layer mask.

  1. Place the redish layer on top and fill entirely with your color.
  2. Create a selection of the area which you want to retain the redish color. Depending on if you want the blending to go down from the current line or up from the current line, you will make your selection end at the line OR higher respectively.
  3. Optional: Create a channel from the selection for later use
  4. Add the selection as a layer mask
  5. In the layers dialog, select the mask instead of the image.
  6. Use the smudge tool and/or a gausian blur to modify the layer mask. Remember, wherever there is white on the layer mask will show through and where the layer mask is black will be hidden. Any grey value in between the two will be some level of opacity.


Note that I have not used PS in 8 years or so and I use GIMP instead, so while the details may be a bit different, the general workflow should remain intact as above.