The way Stack in Leopard assume the first icon of whatever is in the folder of the Stack pretty much sucks and looks horrible. However, this is a way to make them a little less ugly. Optica Optima has a beautiful solution with their beautiful semi-transparent icons.
Download the icons.
Mirror on Justin Allard dot com.

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Getting the icons to stay at the top of the Stack is the real trick, and involves a little a little Terminal hackery. The following Terminal command is an example of what you may have to type.
cd /Applications
touch -mt 202001010101.01 ApplicationsIcon

What the first command does is change the directory of where you are working, so change it to the place you put the icon. If you don't know the path, just drag the folder to the Terminal after typing cd.
The second command uses touch which changes the date modified of the icon to January 1st 2020. Because of the date change, you can sort the folder by date modified and the icon will remain at the top.
Alternatively, you could just name the icon with a 0 as the first character, and sort by name. Use whatever works best for you.

Credit to Optica Optima and XD.