Well, it's me, Red. I came back from the dead to ask a maybe simple question. Didn't know what keywords to search, but what I did try came up with nothing good.

I am unsure how to go about a certain thing with icons;
Let's say I have a square and a rectangle. They are shaded in greyscale colours. They both have alpha masks, evidently from the rectangle.

Is it possible to add any icon (That takes up the full 32x32 grid) that only covers the pixels colored on the square and rectangle, without using more icon states then the original square, rectangle and said custom icon?

A bonus if the custom icon can also be effected by the shape's shading, but that's something I could do, though if it doesn't do it well I might come back again.

You could say it's a universally-usable decal system.