How do you examine 1971's for re-coloring

Interested in hearing from some experts on examining cards for re-coloring. What do you look for. I have a black light but honestly, I'm not sure what to exactly look for. ANy help would be greatly appreciated. Thanks
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1957 Topps 99% 7.40 GPA
Hank Aaron Basic PSA 7-8(75%)
Steve
Always looking for Topps Salesman Samples, pre '51 unopened packs, E90-2, E91a, N690 Kalamazoo Bats, and T204 Square Frame Ramly's