If you need a custom finish for your product, that is no problem. 

In finishing you have two basic options, paint*, and powdercoat, which we can look at in more detail – 

Paint(2K) is more generally more expensive, mainly due to labour.  Skill is required for application.  Paint’s adhesion is superior, finish quality can be superior, and colour matching is relatively cheap.  Paint is more prone to chipping, however, chips are localised, and do not compromise the surrounding area.

Powdercoat is cheaper in bulk, more flexible, requires less skill on application, demonstrates poorer adhesion against paint, and is more expensive with regards to colour matching.  Smooth / gloss surface finishes with powder are largely impossible.

Which should you choose?

Indoor – either method will be more than adequate.  Cheap bulk goods, go for powder.  Colour matching or fancy finishes go for paint.
Outdoor – alloy wheels on cars, either.  Cheap garden furniture from china – powder.  Anything steel (non-galvanised) that you care about, paint.  Complex structures like railings and cast alloy tables can benefit from powder, due to the electrostatic attraction providing non line-of-sight application, however, caution is advised against powdercoating any external steel that is to survive long term.

Colour matching – 
Paint can be mixed to any RAL code.  There is a GBP 40 setup charge for mixing custom colours.
Powder can be bought in to almost a similar, but somewhat less extensive colour range.  There is a GBP 165 setup charge for non standard power colours.

*note –

All finished referred to as “paint” assume 2k, more specifically 2 part epoxy primers, and 2 part isocyanate top coats.  1k “rattle cans” are applicable to home / diy users only, and have virtually no position in the professional market.