Nope, maybe it oxidized or something?

 

Meanwhile... Somewhere in Western Australia...

 

Thought about it, but that would increase the production time from 3 minutes to over 10

 

What colour dial is this?

 

I don't know of any Constellation that used blued steel on the markers, star or logo. I always thought they were white or yellow gold, or at least plated, depending on the particular model.

Given the overall original look of the watch, I think that the coloration is simply from years of accumulated dirt, or possibly a reaction with chemicals in cigarette smoke. It has been known to happen, even with solid 14K or 18K gold. It also looks as if the crystal is not correct for the watch (missing the trim ring). This may have left the case less than airtight, allowing such chemical reactions to occur.

My guess is that this environmental damage can be polished out by a skilled watchmaker without touching any other part of the dial. I'd also recommend new gaskets and water resistance testing when serviced.

Hope this helps,
gatorcpa

P.S. It could also be just the angle at which this picture was taken.