Heat, air flow on the painted surface, humidity, condensation, heat from lighting, many variables can affect the final appearance. I very much doubt it was a mixing issue. The number one suspect is incorrect surface prep and contamination under the topcoat.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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