Hey Wizard,
I'm guessing that you really know cattle are red/green color blind. They were probably interested in your truck because they've been fed out of the back of a truck before. I used to work cattle at rodeos, and a good trick to try is to make the "electric" sound of a cattle prod, that "zzzt-zzzt" sound. If cattle have ever been moved using a cattle prod they remember it, and will move pretty quickly out of your way. You can move Brahma bulls with those things.