Screenshot attached.
Switch to creative mode, open the inventory, go to the "Transportation" list and find elytra. When your mouse pointer hovers over it, you can see that the tooltip for "Elytra" is yellow.
MC-130952
The tooltip for elytra is yellow
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Elytra are an uncommon item, so they get this color. A lot of other items also got colors; see the article on 18w21a.