I had a customer ask for the easiest way to recolor the 3x4" and 6x4" monthly calendar pockets so I thought I'd share a quick tutorial. I know I've done recoloring tutorials before but this one is specific to those kits (though the same principal would apply to recoloring almost any png file - even those that are already colored.) You could just use the paint bucket tool but you'll get some ragged edges that way (that may or may not bother you.)
Once you've opened your file, create a new layer by either clicking the new layer icon in the layers palette or the key combo ctrl+shift+n.
You may need to make sure you have the correct color mode selected. To do that, Image>Mode>RGB Color.
Choose the color you'd like the design to print by clicking the foreground color box.
Activate the paint bucket tool by clicking on it in the tool palette or by just hitting "k" on your keyboard.
Click anywhere on your canvas to fill the layer with color.
Ctrl + G will clip the color layer to your design layer. To permanently merge the color, click ctrl + E.
As with anything in Photoshop/PSE, there are a number of ways to accomplish any given task. This is simply my preferred method. If you have any questions, just ask!