[racket] make only selected color to transparent

From: Jens Axel Søgaard (jensaxel at soegaard.net)
Date: Sun Nov 21 09:45:31 EST 2010

> and I realize that the png files what I used is does not have any
> transparency
> could you let me know how to set a color as transparent as well?

Here is how to do it in GIMP:


Jens Axel Søgaard

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