Replacement icon does not display when in a stack?

I downloaded some icon replacements for folders and I copied them and replaced a folder in the get info for a folder. I then drag the folder with the replacement icon into documents that is currently a stack in my dock and I drag it directly to the dock to make a stack out of it. The replacement icon does not show up in the dock as a stack, it keeps showing the generic folder. Is there a way to do this?

Thanks.