Have you ever used a line art where you need to use lock alpha? Hit that and make sure you color on the layers that have the word "color".
Example: I see you have the unicorn horn layer turned on. Make sure you click the layer below it that says "Unicorn Color." Then, when lock alpha is on, you color on that layer all you like without getting that color anywhere else.
I hope this helps. If you need any other help, just ask!
