Step 6
Delete the background layer, then add a group folder at the top of the layer stack. Shift + click your top and bottom layers and drag them into the group folder. Cmd/Ctrl + click on your new Channel thumbnail to generate a selection. Target the group folder and go Layer > Layer Mask > Hide Selection to trim away the excess areas. Target the ‘Mouse top outer’ layer and draw closed paths around the areas circled in red, make a selection and hit Delete.

Step 7
Disable the visibility of all layers but ‘Mouse back outer’ and clip an adjustment layer by holding Alt/Opt while clicking on the ‘Create new fill of adjustment layer’ icon at the foot of the Layers palette. Select Hue/Saturation. In the next dialog box check Use Previous Layer to Create Clipping Mask. Set the Hue to 171 and the Saturation to 25 with the Colorize preset checked.

Step 8
Set the ‘Mouse back inner’ layer’s blending mode to Pin Light; clip a Hue/Saturation adjustment layer, setting the Hue to 296 and the Saturation to 25 with the Colorize preset checked. Do the same for the ‘Ball’ layer using Hue = 318, Saturation = 31, but leaving the blending mode unchanged.