The Passport card only has black & white photo because the picture and information is printed/burned on a laminate and then affixed to the card. I know this because the laminate on my Passport card peeled off and exposed the card. I have also seen the blanks of the Passport card.

At least, the picture and information on the NGP is burned onto a polycarbonate. I would rather have my information on a sturdy surface as opposed a cheapo laminate that can be peeled off or printed on something that can be washed away if exposed to water/excessive moisture. Granted, damaged outer covers or visa pages can render a passport useless.