Peter Bargh explains how you can use the valuable Layer Mask option of Photoshop to make better colour changes and selections, in this step by step image editing technique.
Explaining how to do selective coloring using the History Brush and here's how to do a similar job using more controllable Layer mask.
Having more of a handle on using layer masks will make you more aware of your layer palette. Learning about converting and doubling images into a new layer. Peter Bargh is a bit more indepth about the control purposes of the adjustments.