Ok, i've searched this forum, and the web as a whole to try and find a tutorial on colour trapping in photoshop or illustrator, but can't find anything.
What I do at the moment in photoshop is select one of the lighter colour layers (once they're seperated), expand the outline by a couple of pixels, then fill the expanded area with the same colour. This works fine, but I only want to overlap the layers on the edges where they meet, not the whole layer, if you know what I mean. Any thoughts?
Yeah, it can be a fucking puzzle. In both respects.
Try your best to incorporate trapping as you design or part of the design itself to make things easier. You'll prolly be end up selecting by color, expanding pixels, fill on a separate layer, select the color(s)' edges you want removed and clear it out?