When I dye my shulker boxes, if I log out with the Shulker box placed in the world the color of dye is retained when loading the game save. But if the Shulker Box is placed in an End Chest when save is made and then reloaded, all dyed boxes are white upon loading.

Minecraft is Build: 3644540, Branch: edu_r12_cw. Build date 2020-01-23