In the daytime, orientation is relatively easy for model planes which aren't too far from the controller. Multirotors are more difficult, and when yaw control is not set to compass-fixed-bearing, can be very difficult to point. One simply solution is to always use a set of LED lights, in different colors, on each arm.
Model planes are difficult to see at night, but at least the general flight direction can be sensed pretty reliably from the orientation, with even minimal lighting. Multirotors are damn-near impossible without information being encoded in the lights themselves, since color differences in paint/anodizing on the arms is drowned out by a bright sky background at a distance during the day, and by the lights themselves at night. Multirotors may color one arm differently and designate it as 'forward', or they may do a forward-back or left-right color contrast.
The custom on full-size aircraft is a red light on the left side, and a green light on the right side. This allows aircraft in a potential collision course to determine which way the other plane is heading (coming or going), and which side to pass it on even in the event of gross speed differences.
- Multiwiicopter Andromeda LED board