|Colorizing your engine bay accessories is a lot like getting a tattoo. Done well it can be attractive and add visual interest; done poorly, and it becomes an unambiguous statement of bad judgement and poor taste.
The beauty of an engine bay is derived more from it's display engineering excellence. A clean and well sorted engine bay doesn't require, nor should it depend upon, garish accessorization. IMO most owners do their car's appearance a disservice when the rattle can spray certain parts just because they can be unbolted; or are removed as part of a major service overhaul.
If I were to add a color the engine bay, it would be based upon the exterior or interior colors already present on the car. The rule of thumb I've always used is that if a repainted or colored part is too bold and is the first thing the viewer's eye moves to, then it's overdone. The addition of color needs to be subtle and sublime.
The knowledgeable enthusiasts should be invited to first scan the engineering and mechanical aspects of the bay, and only then, be rewarded with a visual treat of color. They're VG30DE(TT)s...Not kaleidoscopes.