all the bolts on the door hinges are painted in body colour as they are painted with doors installed at the factory.
The only 2 or 3 bolts you see in yellow zinc galvanize are the door holder bolts - make sure to use threadlock on them when reinstalling otherwise they will rattle.
The striker plate and the two screws holding it are usual silver shade zinc plated - they would require an impact driver to remove and install.
What bolts are you trying to coat? - btw manghopir, bihar colony, al asif sq, godhra (near sunday scrap market), all have these small "kaarkhanay" doing such jobs. - much better competition and pricing.
There are tons and tons of them in Karachi.