I have been told that it depends on interior color. FOr instance, on a Candyapple Red car it would be black if the interior was black. Any other interior color it would be white.

So some red 1968 GTs came with black stripes and some with white stripes.

Sounds goofy but all my research seems to back this up. I know that C-stripes came in colors other than black and white. Don't know what combo of interior/exterior colors got you the other color stripes.

 

My 68 Diamond Blue with blue interior has a blue "C" stripe. It also has a black vinyl roof.

 

OK. After posting had a thought that I had seen a matrix on this... dug around and found the reference. It notes "recommended" accent stripes, not C-stripes, but one could "assume" the color schemes would be the same for stock factory add-ons for GT stripes:

A - Raven Black - White (but gold used with black, saddle, parchement and nugget gold interiors)
B - Royal Maroon - White (but gold used with saddle or nugget gold interiors)
D - Acapulco Blue - White
F - Gulfstream Aqua - White
I - Lime Gold - Black
M - Wimbeldon White - Black (but gold used with saddle or nugget gold interiors, red with red interior only, blue with blue interior only)
N - Diamond Blue - (red with red interior only, blue with blue interior only)
O - Sea Foam Green - Black
Q - Britanny Blue - White
R - Highland Green - White (but gold used with black, saddle, parchment and nugget gold interiors)
T - Candyapple Red - White (black with black interior only)
U - Tahoe Turquiose - White
X - Presidential Blue - White
W - Meadowlark Yellow - Black
Y- Sunlit Gold - Black
6 - Pebble Beige - Black

Anyone know if this is correct?

 

Somewhere in my area lurks a choice 68 Highland Green Mustang cpe with the Sprint pkge-the one with the grille lites, argent SS wheeels.It has a gold C-Stripe. I remember seeing a black 68 Cvt at Pensacola that had a gold stripe, also.