As Hemkiller stated, body color determined what lower accent color, Tu-tone hood, and body side tape stripe were defaulted to.
All '71 Mustangs with the lower accent paint received black paint (Along with black body side stripes and Tu-tone
hood paint if equipped). The exceptions are "A" #1724 Black, "C" #3542 Dark Green Metallic, "J" #3657 Grabber Blue, and "6" #3077 Blue Metallic. These four colors received Argent paint (and stripes if equipped). For '72/73, color codes "4Q" #3542 Dark Green metallic, "3K" #5210 Blue Glow, and "4C" #5072 Ivy Bronze Metallic were added to the argent-only list.
I've seen Grabber Blue and Blue Metallic cars with owner installed black paint and accents, which look good. I feel the black does do a better job of hiding road tar and other debris thrown up by the tires. Another combination I've seen that looks good but was never offered by Ford is red with silver accent paint and stripes. Years ago, I took the photo below at a car show sponsored by D & D Motors in Greer, S.C. It illustrates the silver stripe and accent colors on red. It sure looked good to me. The car was not part of the show but was doing some "Protective" parking. The show was at the Ford dealer behind the Po Folks sign.
Unless you are doing Concours, paint or stripe it the way you like.
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