Used the magic wand tool to select certain sections on the background layer. Then clicked new layer and used the fill tool to add colour.
Changed the colour of the black outlines by clicking the adjustment icon – Hue/Saturation, ticking Colourize option and playing around with the sliders.
All different colour layers need to be printed separately in black. Made a copy of the colour layer (Duplicate Layer), clicked Lock Transparent Pixels icon. Edit – Fill. Change Contents to black from dropdown menu.
Selected everything in the colour layer and shifted it all slightly to create a new effect. Looks pretty snazzy. Also shows what the print might look like if the collaboration is slightly off.
Knocking out & overprinting: Multiply option shows you where the colours will overlap.
To get rid of the overlap colour: Selected everything on the pink layer. Made layer invisible. Clicked yellow layer. Deleted selected.