With eleven long-haired Friends of Jesus in a Shar-Trans
microbus

The story:

I thought "Rubber Duck" was specifying the manufacturer,
rather than the color, of the microbus. (He does mention the
manufacturers of the three trucks that initially formed the
convoy: his, "Pigpen"'s, and one other.) I didn't know at the time
that no such manufacturer exists. And it sounds out of character
for "Rubber Duck" to describe something as chartreuse.