Even just one player using the cover, when using Elytra, it changes color for all players, and the correct thing is only the player who is with the cover, change Elytra's color, not to mention that if you have another friend with a different cover, interference happens, Elytra changing the color all the time.

So fix that and make the color of Elytra only change for whoever is using the cover. Oh if I've been wearing a cape, Elytra just changes color for me. And if my friend uses another cover different from mine, his Elytra changes color to his cover getting different from mine.