1956 Topps Kaline #20 in PSA 8 - White Back, Gray Back Values
The Pop Report lists 239 White Backs with 38 higher. There are 49 Gray Backs with 9 higher. The Price Guide is $325, but doesn't distinguish between the two. I know that other years, 59's for example, have Pops for generic backs, greys and whites for #'s 199-286, so this fairly recent phenomenon probably affects value very little, since generic backs can be resubmitted for a white or grey designation if the collector wants.
1956 Pops list no designation EXCEPT white or grey. The huge number discrepancy has another, visual difference: the front of the rare greys has super-saturated color, unlike their more common counterparts.
I'd appreciate any input on current market values. Thanks.