Metal

The metal lines are by far the easiest of the three types of line to recognise. Any area of the die shot that is speckled white is a metal line. Some are thin, but some are very thick:

These metal areas are semi-transparent though, and so we see other features such as the edges of the poly and diffusion areas underneath the metal line, along with the pink and green tints from thin films effects around those edges. Even these features have a lighter shade making it easy to clearly identify what is dark versus what is light on the die shot. If all the darker colours are replaced with black and all the lighter colours with white then you'd end up with a diagram such as the following that shows only the metal layer in white: