Pesky blue glow around item slots?

[TurboCrackers]

Hi everyone! I'm creating an inventory mod where I combine all bags into one, and I'm having an issue where when I create each slot, it gets a blue glow around it (I'm using ContainerFrameItemButtonTemplate for each slot). When I hover over each button with my mouse, the blue glow goes away. However, I can't seem to figure out what's causing it to be there in the first place. Any suggestions?

[MunkDev]

BattlepayItemTexture

And this is why it goes away OnEnter:

-- in ContainerFrameItemButton_OnEnter
local battlepayItemTexture = self.BattlepayItemTexture;
... 
battlepayItemTexture:Hide();