Highlight section on image with transparent color

Create a Selection (Selection Tool of choice), then, with that active, create an Adjustment Layer, say Hue, Brightness, Saturation, and that will be applied to the Selected area. Now, if you wish to maybe lighten, or darken the area outside that Selection, just hit Ctrl+Shift+I, to Invert the Selection, and apply that Adjustment Layer.

Good luck, and hope that helps,

Hunt