Good point. Color is important. I think we also oughta consider canvas albedo, time of day, lattitude, prevailing wind direction, relative humidity, terrain gradient, soil type, local topography, rope composition and condition, shrub / bush species, age and health (to determine suitablility as temporary anchor point), likely duration of stay, etc.

Civilians think this stuff is easy. Kids, do not try this at home. We're professionals.