I start with choosing an element I want to recolor and open it up. If it's already colored, you can either desaturate (layer>color>desaturate) or leave it as is for a different effect. The above is the image I chose for this tutorial. I added the black background for both this tutorial and also for quality control. I delete this layer before saving as a png.
Create a new layer and bucket fill with the color you want to use. If you are not working with a specific palette, you might want to try a shade or two darker since the results are better. The image above points to the two items that make this work, layer mode (normal) and opacity (100%). Before you change these your image will be just the solid color you bucket filled. Once you change the layer mode to overlay or burn you'll see your element pop back up.
This was done with 1 bucket filled layer set at 100% opacity in overlay mode.
This one is 2 layers, both 100% in overlay mode.
This has 3 layers, 100% overlay mode.
I used one bucket fill layer, set at 100% opacity and layer mode burn.
Final example, 2 fill layers, one set at burn and 70% with the other as overlay and 100% opacity.
When you are satisfied with your coloring, test your background layer with different shades to see if it's what you need for your project and to look for brightness issues, stray pixels, etc. Delete your test background and
merge visible layers*. Do NOT merge down if you have more than one fill layer. It will change your results. You can merge down one at a time if you select the fill layer directly above the element. Merging down one fill layer onto another will create a solid filled image at normal layer mode again. NOTE: Use caution with merging visible layers if you are using this technique while creating a finished layout instead of a simple element. You can hide the layers you are not using by clicking on the eye in the layers dialog box. This is what I do when I am recoloring my photo book frames with the ribbon. My ribbon, rivet and paper take different amounts of shading so I assemble and recolor this in layers. My template has been saved as an xcf file so I can use it and alter it for other kits. You can see an example of it's layers in the image below:
The layers marked tint I will alter the color of to reflect the palette I am using, or I will replace with background papers or patterns. I keep my shadows so I don't have to create them again as well. Above the page frame layer is where I would place any texture overlays if using a bucket fill in order to add a pattern or texture. This example only shows 3 tint layers and all in a different color. I did this to get a more natural look. What it doesn't show is that I may or may not use more than one ribbon, rivet or page tint for each detail. This is where I play the most.
When I am doing the ribbon tint, the whole image will show the effects. I will merge down the ribbon tint to the pinch ribbon layer or I will hide all layers I am not actively using and use the merge visible method. Then I'll hide the finished section and unhide the next part of the layered element, in this case the rivet. Once I think I am happy, I'll unhide the ribbon to check for harmony, hide it again and merge my rivet parts. I'll finish off by repeating these steps with the page section. I'll unhide all, recheck and if happy, merge all, save as png and make sure to save as a different name as your template! Nothing more irritating than to overwrite your template, which is why I copy and paste the templates being used into a folder for the kit I am creating. This keeps from losing my template. When I create a new element, I save it as a template in case I need to tweek it or want to use it in another kit in a different color or style.
*Merge Visible Layers and Merge Down are two different operations and are listed as such on both Gimp and PSE. If you pick the wrong one, you can undo it. Once you see what each does to different layers, it's easy to understand which one to pick.