About 2 years ago (at any rate, before the pandemic) I tidied up some of the conversions and gave them a repaint. I painted the armour white and washed it with strong tone, for a grimy finish. While this made the conversions stand out, it did make the models just look a bit messy, and they didn't fit with the rest of my army, who have a roughly Black Legion colour scheme.
So, I dismantled some of the models where necessary, and gave them a repaint. They all got black armour with brass trim, but on each model I added another colour, usually to highlight some interesting (often converted) feature. So here they are!
Left to right: Bulked out body and weird tube - this guy had had so many repaints and conversions that most of the detail on him had vanished under glue and inept knifework. He's also blurry, which might be for the best. Spindly legs - these came from an ancient plastic genestealer. His head and body are one piece. I think his axe came from a chaos knight. Big gun - this chap is unconverted and solid metal. He's a real lump. Getting a decent picture was really difficult.
Left to right: Fly head - the head came off a Kill Team Rogue Trader model. I really like it, especially the arm holding his gun, perhaps pointing out a target. Pincer arm - this chap has an old arm from a chaos mutations sprue and a head from a chaos warrior. Snake body - this was originally the lower part of a Slaaneshi warhammer chaos champion (I think) that I chopped up many years ago.
I've got a few more of these odd conversions and old marine models. Yes, they're a bit small and wacky, especially compared to modern chaos marines, but they have a certain Realm of Chaos charm, and I like the colour scheme.