What is the quickest way to achieve this? Multiple layers? Layer masks?

Open the color image you wish to modify. Select all and COPY the full image Now use Mode and reset the color to Grayscale, say "Yes" to removing all color. The image goes grayscale. Tweak or adjust the black and white until it suits you. Return to MODE and return the image to RGB Select the Move tool (Tap: "V") and then PASTE The original color will return to the file on a new layer.