Assuming they're metal, sand, etch-prime (available in aerosol) , spray them black. There are self-etching aerosol paints in different colours. Key is to use a good precleaner after sanding/before priming...gets the contaminants of the surface( grease from your fingers, dust, ect.), and gives the primer better adhesion.
Have a look in Napa or any automotive store for an adhesion promoter/primer. There are some available that are 'wet-on-wet'. Spray on , let it flash for 30 minutes, paint...no sanding.