My suggestion would be to use Pactra Racing Finish paint. Made by Testors (same people that make Floquil and Polly Scale). It comes in various colors, but I have found that Black, White and Yellow will work for most hand rails made from Delrin. The paint is formulated for Lexan racing cars. It will not flake and has great "flexibility". Personally I have done twenty plus engines with it and nary a problem over the years.
As always, your mileage may vary...
As always, your mileage may vary...