If you have all the metal for a given job painted at the same time, in a single set-up, the coating should be uniform.
However, most paint manufacturers expect their paints to vary a little from batch to batch, usually less than 2 delta E as measured by AATCC Test Method 173-1998.
This can result in a barely noticeable difference in color between batches of paint.
The differences can be larger with a translucent or metallic coating, however. Learn more about metallic coatings.