3 Colour, Select and repeat
Now you’re free to colour your image, using your preferred tool of choice. Any colouring will, of course, be applied to the renders layer only on the selection that you’ve made. If you want to make it a little easier to see what you’re doing, you can toggle the marching ants visibility using View> Selection Border. Once you’ve finished with a particular colour, you can use the Magic Wand again to select a different area and continue to colour. Colours on the ‘renders’ layer will have no impact on your selections.