Basically, I tried to fill an area from ~ 0 ~ to ~ 255 ~ with red_shulker_box
It worked fine: the shulker boxes were red...
Then I tried to fill that same area with orange_shulker_boxes! It said that the blocks were filled, but they were still red!
When I removed the "red shulker boxes" they did orange particles! This bug works with every single color!
Also, the bug gets fixed when you reload the game! I tested it on a normal world and the bug was there... but when I tried to test it on a void superflat world the bug was gone! I think it's something to do with the lag, when you fill an area with shulker boxes and the game doesn't have time to register all the changes of colors! I made a video to explain it better!
Here is the video: