Horizons Unlimited - The HUBB - Why does my XL600LMF have a red frame?

Hi all, I’ve recently bought an old (86) XL600 LMF and am loving it! What a cracking bit of kit, relaxed, bullet proof (I hope!) and cheap! bier
I’m sure I will have loads of questions coming up but for now there is one thing that I am really trying to work out……..
Why has my LM got a red frame?
It’s a UK bike & has the twin headlights, big tank & red engine (which has been re-painted but was also originally red judging by the paint underneath)
I have seen loads of pictures of bikes just like mine but never with a red frame!
Having stripped the tank & body work off to sort a leaky carb I am 90% convinced the paint is original as the bits under the tank, round the headstock & under the seat all look original?
Also the frame plate is in-tact & I can’t see any trace of overspray or re-fitting and when I was changing the oil a flake of paint cape off the down tube fight down to the bare metal & there is only red paint in the flake (no white underneath)
I am guessing it is one of 3 things.
1. I am a Muppet with the observational skills of a mole & it has had its white frame re-sprayed (with a bear metal strip hence no white under the red)
2. It is a super mega rare “red framed special” which collectors will sell their first born child to buy & my £600 hack has now become my retirement plan
3. Red frames were perfectly normal & its coincidence that Google images does not return any on the first few pages.
Any help working this out would be gratefully received!
I’ll try to upload a pic once I work out how!