You may notice, some products after hot-dip galvanization (HDG) coating, even in the same facility, using the same process, may look different from others. It can be noticed that some of the products will be much brighter and others much darker.
There is nothing wrong with the product nor with the coating and any difference will depend on the product steel.
Variations in
coating thickness
and the content of silicon in steel may cause different appearances on the finished product.
Please refer to this article for more details: The HDG Coating (galvanizeit.org)