Blue Seamaster logo on caseback?

I have been eyeing a cal. 1020 for a while now and have stumbled across one that I might be intersted in.
However, there has been one thing holding me back from pulling the trigger and that is this weird coloration on the caseback.
Is this something Omega did back in the day or did the previous owner do this for some odd reason or is the caseback just a weird fake?
Also, is there a waterproofness rating on this guy? I know in general you shouldn't really take your vintage watches to their original depth rating but knowing that with some new seals I can take it safely in the pool or at least wash my hands without having to take it off every time will make me feel more at ease.
Thanks for the help in advance

Alright cool, I didn't know! thanks

That protective layer comes in different colours and can be bought at Machining supply stores.

I think that usualy new watches came with that blue coating..