Photoshop change Background color

Duplicate the file so that you have a backup. Add a layer on top and fill it with a bright green. Change its fill mode from Normal to Overlay. Adjust its opacity until it looks right on the parts that matter. Next, erase the layer over the mask’s label and other areas where it looks wrong. Merge the layer down over the first layer. Add a new layer behind the first layer and color it red. On the merged layer, select Replace Color and replace the green color with a transparent color. Adjust the replacement threshold until the image looks correct over the red layer. Make any last corrections by hand. Delete the red layer. Save as a png with transparency on.