Today's tip is Match Color. This is an AWESOME tool that I only learned how to use a few months ago. I keep finding myself needing it, though, and I love it!
Start by opening the ribbon that is the shape you want, but the wrong color. Then open the page of the color you DO want. Make sure you have the ribbon you want to change active.
Now, go so Image> Adjustments>Match Color.
Now, matching color does that--it matches the COLOR, not the pattern. So my ribbon is green, but it will not have the pattern my green paper had. It doesn't always work very well with changing the color of elements like flowers, etc--though you can adjust the FADE level to make it look better.
You can also do this with just a colored box. Lets say you love a certain element from a kit, and want to use it in another kit or just on it's own. Create a blank page, then draw a square shape of exactly the color you want. Flatten the image (Layer>Flatten) and crop it so that the page is all one color. Then follow the same steps.