How to make a red reveal message?

I am trying to create those hidden message pictures where you see a message when you put a red transparent filter over it. There are existing techniques on how to do it in Photoshop, but I don't have Photoshop. I do have paint.net, and if there is any way I can create a red reveal message using Paint.net, then... show more I am trying to create those hidden message pictures where you see a message when you put a red transparent filter over it. There are existing techniques on how to do it in Photoshop, but I don't have Photoshop. I do have paint.net, and if there is any way I can create a red reveal message using Paint.net, then I wouldn't have to look farther. I also have to ask this in the board games category, there wasn't any categories about photo editing and some board games use red reveal messages.
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