The bug
The names of the contained items should be white, yellow, cyan and magenta respectively, however they all display as the same colour.
The ominous banner's name displays normally, however.
Steps to Reproduce
Give yourself a shulker box that contains multiple items with different item rarity colors.
/give @s minecraft:shulker_box{BlockEntityTag:{Items:[{Slot:0,id:"minecraft:enchanted_golden_apple",Count:1b},{Slot:1,id:"minecraft:elytra",Count:1b},{Slot:2,id:"minecraft:beacon",Count:1b}]}}
Hold your mouse cursor over the shulker box in your inventory to display its tooltip.
Take note as to whether or not shulker box tooltips display item rarity colors.
Observed Behavior
Shulker box tooltips do not display item rarity colors.
Expected Behavior
Shulker box tooltips would display item rarity colors.
Can confirm for 1.13-pre5