Help me, Readers!

An old friend of mine e-mailed me thusly:

Hey, I was wondering if you would know which older movie featured a battle scene wherein the protagonist and antagonist morphed into various creatures…but since it was well before morph technology, the screen showed neon-like outlines of the animals (in electric blue and neon red, as I recall). Was it Clash of the Titans ’81? A Conan movie? Something else entirely? I saw that little bit of the movie as a kid, and it has stuck in my memory ever since. Do you have any idea what I’m writing about?

And I can kinda picture a scene in my head like what he’s talking about, but nothing specific enough that adds up to a memory. I know I have a number of readers who ought to be right up on their late 70s/early 80s F&SF flicks, so can anyone shed some light on what Mark’s movie might have been?