Quark adds colored runes to change the color of enchanted items.
When the two items are joined the color of the elytra is lost and takes the original violet color of an enchanted item (or the color of the armor if you don't have any item in hand, I know it's strange)
When the items are separated it recovers the color, that works fine.

I don't know if it's possible but it would be great if it works with the color that was given with the quark rune.

I use forge 1.18.2 40.1.19