I am pending to buy a American 57 reissue but I can't seem to know the exact date which the guitar is being built.

Serial V058107.

The body has aged from a sonic blue to a foam green, is that normal?

Aaron

As fender write for dating Vintage series , the only way to date year is to check date on the neck .

Not easy way !
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http://www.fender.com/en-GB/support/art ... uct-dating

V + 5 or 6 digits (American Vintage Series except ’52 Telecaster, which uses a five-digit number stamped into the bridge plate)

(for American Vintage series, check neck date for specific year)

I don't know if that's normal for a Reissue,but I had a '65 Sonic Blue that faded the same way and have seen other vintage Strats do it because of the base coat I've heard.
Either way,I think it's a cool thing.

I have a 1991 AVRI 62 Reissue, also with a V05 serial number. There usually is a mfg. date stamped on the end of the neck, although mine was too blurry to read. If you don't want to pull off the neck, loosen the strings and pull off the pickguard - check the codes on the pots. Mine were dated 1990 and 1991, and I'll bet yours are too.

As for the the finish, nitro can age in different ways - not so bad in your case!

mcmacguy ,+100 for the code on pot