Careful application of a strong cold blue, like Birchwood Casey's Super Blue using a Q-Tip should cover it up just fine. Just don't overdo it or you might affect the existing finish.
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D. Kamm
USGI M1911/M1911A1 Pistols Website
http://usgi1911.tripod.com
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D. Kamm
USGI M1911/M1911A1 Pistols Website
http://usgi1911.tripod.com