Studies done in the transportation sector prove the best color for high visibility worker clothing is fluorescent safety orange because that color is the most visible from the greatest distance. A fluorescent yellow-green color, while not as visible at distance, offers better night visibility and is also a better choice for signage because it provides more contrast for lettering.
Some groups of divers have informally assigned meaning to bag color. Shooting an orange bag or marker is supposed to indicate a normal situation to surface support. The appearance of a yellow color may mean that the diver has an abnormal situation and requires assistance from the surface. However, there is no color standard along with considerable confusion about color.
Our recommendations: If visibility is most important, then orange is proven by far to be the best color choice for distance visibility during daylight hours. Choose yellow for night visibility, or for a day and night compromise we offer a marking tube that is yellow on one side and orange on the other. We respectfully suggest reconsidering any dive plan which depends on the color of a bag to signal for help.