Is there any way to do this? When I’m modeling I like to create a bunch of material slots just to add some basic color, then after I mark my seams and unwrap I noticed that I can export the UV layout with a fill opacity of 1, which saves a lot of time when painting the texture, however I’d like to get the edge lines on a separate layer than the fill colors. Is there any way to export just the fill colors without the edge lines?
I do not know exactly how to do what you are describing. However, an alternative might be just selecting your object, switch to edit mode (Tab), go to materials, click + to add a material, Click New, click the white box next to color and choose a color. Then click apply. Your object (or selected faces) has been m colored. Hope this helps. 
Thanks, what you’re describing is what I actually do in the beginning. What I was working on was a simple low poly character where most of the color was done by filling in faces with solid color, using different material slots. At the end I wanted to add details using a texture, so I decided to unwrap it and export the layout to create a bitmap texture. Its nice that the layout will export with all your current material colors in place, however it places the edge lines on it as well. So when you open it say in Gimp or Photoshop you would have to some way remove all those lines. I normally keep my edges on a separate layer in my image editing program, then paint color and details in other layers on top of that. Then when I save the image I just turn off the layer with the UV layout on it.
As I continue to work in Blender I’ll probably find a workflow that works better because there are a ton of options in the UV editor I don’t use.