If you dragged and dropped the PNG into a new Photoshop document it would get placed as a smart object and you would have to add a layer above, or rasterize the smart object, in order to paint color. If that was the case, the color problems could be caused by transparency effec...
What does mock-up mean? 1 :a full-sized structural model built to scale chiefly for study, testing, or display. 2 : a working sample (as of a magazine) for reviewing format, layout, or content. What is a mockup image? A mockup isa digital rendering or model of a product, either ...