Color choices are often a matter of personal preferences so it is hard to give feedback on that. If you have two layers that are accidentally merged, one way to “unmerged” them would be to try to use the lasso tool, circle ONE of the two elements, then in the Layers palette, right-click on that layer, and select “Promote selection to a layer”, then reactivate the initial layer and hit DELETE. That can be done when the elements are clearly separate and not overlapping. And don’t worry about deviating. The idea is to do the exercise and practice using the tools.