From your image, you did it exactly as it should to show that yellow image on top. The reason the image is faint is because the “unmasked” part is grey instead of white. Remember: Black will block, white will show (and grey will show partly). If you want the grey to turn white, you can either select it (with the magic wand for example) and fill it with white, or you can increase the contrast of that mask layer.
Is that addressing the issue?