anyone know how to draw image in one color?
or make the image transparent? or whatever to change the image into something different from the other
The easiest way to do this for something static like a map editor where your images can be prerender is to use the pixelGrabber class. After you have all of your pixels in an int array simply pass them through a color parser that modifies the pixels that aren't transparent to one set color (red). Then call use the memoryImageSource class to create an image out of it. This image won't be accelerated but if you then copy that image onto a offscreen image through createCompatibleImage(..) you can gain hardware acceleration.
You can find many examples by doing a search for PixelGrabber. They will show you how to do the shifting to set each of the Red,Green,Blue and Alpha's of your pixel. I also have some code I could dig up if you can't find anything useful and you decide to use this technique.
There are better (memory wise) ways to create this effect, but this is probably the easiest and a map editor shouldn't be too memory intensive.