When the ruby Eyeball and Aquamarine fuse into Bluebird Azurite their gemstones change color. Unless I'm mistaken no other fusion has affected the color of the component gems' gemstones. What makes this fusion different from others that they manifest this change in the gemstones?
Opal's and Bluebird Azurite's component gems are just mimicking the appearance of their fusion namesake, the same as any other fusion's component gems do. It did not strike me as unique or unusual in any way. Not a big deal, just depends on how you look at it I guess.