RockChucks out of sight, out of mind is a good mention.
I've not really conducted any serious research, but it seems my barn sized white crew cab 350 and my white Toyota Land Cruiser are both pretty good at sending pronghorn over the horizon. More sedate colors and smaller rigs don't seem to instill as much fear. If any rig is stock still, however, they fail to notice it. Returned and slammed the tail gate on my buddies fire-engine red Ford, and two pronghorn stood up that were bedded in the tall sage about 40 yds behind me.
Another thought related to their poor eyesight in the earliest and latest of hours. One might be pushing the boundaries of legal shooting hours, but a wide open approach in the very last minutes of daylight can go unnoticed until one is well inside of rifle range. Might help too to have the brightest of the horizons at ones back. I was helping a newbie hunter once and we took that tangent on a wide open lake bed. At about 60 yds I was sitting him up with a rock or two and my pack frame after boldly traversing about 300 yds. Something else spooked the group, and we were nearly run over. At 10 yards, I'm not sure I could hit a pronghorn going wide open. They can really pick them up, put them down, and always show us just one more gear.
I've successfully used the same approach on deer. Not tried it with elk.
Downside is one might be working up an animal in the dark.
