I obviously could be wrong, but to me there is no question it is sun faded. Here's a random 1963 Mantle from ebay...
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Like your scan, the blue circle is still blue, but yours is a very faded blue (which shouldn't/wouldn't have been affected by a dearth of yellow), and the rectangle 'text box' is a different shade of blue than the circle, and you can 'see' some green (depends on how good someone's vision is, I guess) there. It's subtle, but it is a lighter, bleached out green (same with the under side of his hat). Plus, as was implied earlier, the entire card is lighter all over and across the entire color spectrum, telling me it either spent a lot of time in the sunlight or was held by some bikini babe in a tanning bed (wanted to sex up this post a bit).