Now, the color of Mythic Keystone's doesn't appear.
Because, the quality of mythic keystone from GetItemInfo(KEYSTONE_ID) is 1.
And GetItemInfo(KEYSTONE_LINK) doesn't work.

so how about change the line 368 of widgets/ItemButton.lua

from
local _, _, quality = GetItemInfo(itemId)

to

local _, _, _, quality = GetContainerItemInfo(bag, slot)

The change you suggested also fixes the border color of Battlepets.

This is great. I knew something looked off. Didn't realize what it was until I saw this.