Well I was not looking at that hatch.
The curved surfaces of the cab you can see the blue showing thru... looks like soot to me.
This is the old scheme... look at the other picture... thats the one lionel model is.
I will go look for some other pics... the other pic kinda looks like blue at the front edge, but its really hard to tell. This cab surface is not as nicely finished as the piston housings that are clearly black painted...