Dude :/
http://www.hiveworkshop.com/forums/icons-541/btncloakofshadows-209834/
Here's an example.
Download and unzip it.
You get FOUR .blp files.
You only need at least 2 of them though (Only take into consideration the BTN and DISBTN ones.)
One of them will be called BTNCloakOfShadows.blp and the other DISBTNCloakOfShadows.blp
Import BOTH icons with the Import Editor.
They will be named war3imported\BTNCloakOfShadows.blp and war3imported\DISBTNCloakOfShadows.
Rename them to:
ReplaceableTextures\CommandButtons\BTNCloakOfShadows.blp
ReplaceableTextures\CommandButtonsDisabled\DISBTNCloakOfShadows.blp
Now, when you want something to have this icon, you give it this: ReplaceableTextures\CommandButtons\BTNCloakOfShadows.blp
The game will automatically create this: ReplaceableTextures\CommandButtonsDisabled\DISBTNCloakOfShadows.blp instead of displaying a green icon.
The reason green icons get displayed is because most users don't know that they should import the files and change their paths like this. The game searches for ReplaceableTextures\CommandButtonsDisabled\DISBTN___.blp, gets nothing, and thus, displays a green default icon.