I just found this thread and am thrilled. Like you Harada357, I much prefer retro. I haven't been impressed with much of the science fiction hardward offerings for the past few years.
I love what you've done with the base gun and converting it towards something in the style of that Flash Gordon comic.
You should drop Steve Neill a note. He's back on the boards I believe. And he's currently working on a retro '60's "Mars Attack" film based on the original cards. He's also a wealth of information and enthusiasm for anything science fiction. He built a beautiful model of the original Doug Drexler designed ship for "Space Command" before Mark took the show in a different direction.
My suggestion for the paint scheme would be trying to the metallic gray mentioned earlier in combination with the brass / copper color. I really like the metallic blue / black combo. Or maybe add some silver. To me, the metallic blue doesn't go with the brass / copper. But that's just my opinion. It's your build and as you mentioned, you can have multiple variations.
This is a really inspiring build. Old-school ideas and old-school techniques.
By the way, the Rhino images you did are also brilliant. It reminded me of one or two of Ralph McQuarrie's sketches for Han Solo's gun as seen in "The Art of Star Wars". Although your design is brilliant. I'd love to see more work done on those as well.
Ted.