They put a gun rack or muddys on them, but that's utilitarian. Maybe the mud flaps with Yosemite Sam are a bit of personal expression. But, you never get a truck painted in bright yellow. At least not any self-respecting Louisiana farmer. If you tried to go hunting in a bright yellow truck, you'd have to park it in the next town for fear of scaring off the animals.
Color symbolism is steeped in history.
Moods and feelings are affixed to colors that cross generations and cultures. Yellow fever, yellow flu, yellow jacket and yellow pages are listed after yellow. But, yet, it's bright, vivid and yanks at your eye like a fishhook. It almost demands that you look at it when it passes. To get that same reaction from passersby, you could stand naked in the street.