Slight discoloration bottom of PC?

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Is it normal for the gold connections at the bottom of the cpu to be slighty lighter (less golden) in color than other parts?

I was curious. I some how bent the mobo pins, no idea how, I was careful. I'm assuming the CPU is fine but have wait few days for new mobo.. I was switching processors (both used). So I'm not sure how long discoloration been there. I assume since its not brown or black its just from "use"?

 

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I never took time to inspect the underside of cpus, so I'm basically wondering if this is common.