In my Channels tab (above) , you can see that in order for me to separate the different elements of the image, I've created a "Flats" Channel.

This will be useful all throughout the coloring process, so if you don't know how to make a Flats Channel, you might want to check out the tutorial I made for that first.

Otherwise, If you already have an image that has these elements set in, then let's continue on.