Say I had access to a full sus frame, but it’s a crappy white colour in its entirety (including vinyls) and I wanted to spray it another colour. What’s the best way of going about it? DIY? Paintshop? I’ve heard stories in the past of paying to get something done and then all the paint cracking as soon as pivots/bearings/everything is screwed back into the frame. What’s the best way of combatting this?

Cheers.

Powder coating has worked for me, there is an (unquantified) risk that it may daamge the alu.

DIY may look OK initially, but takes ages and won’t be durable IME.

DIY is fine as long as its given long enough to harden off. (6-weeks). It is bloody hard work. I’ve done a couple & the best results were with Plasti-Kote, not Halfords knacker-lacquer.
But it wont be anywhere near as durable as powder coating. Frame will need stripping to bare alloy to powder coat. Also crucial to ensure any mounting surfaces/threads are kept clean. Cured powder is very difficult to remove, & even if masked off I’d factor in getting the b/b threads run through by your LBS, along with disc mounts faced. A good powder coaters will have high-temp masking tape to keep areas clean, but a general insustrial coaters will be unlikely to want to faff about. Heat is also a factor, I wouldnt bake an alloy frame above 200c as it could affect the heat treatment. A good, experienced powder coaters will know about this stuff anyway.
You could rub down to give a nice key, & get a local car body shop to paint it with two-pack. Obviously your tied to what colours they have, & two-pack paint is very expensive to buy. In theory two-pack should be less likely to crack as its not as thick as powder coat.
You could always strip & polish it…