MS Paint has some hidden tools that are not widely publicized. In order to find this cache, you will need to use the hidden color replace tool. The color replace function allows you to swap one color in an image for another. It is similar to the eraser, but instead of getting rid of everything, the replace tool works on one color at a time.
To find the coordinates use the green rectangle below. Either save the image and open it in Paint, or take a screen shot of it and paste it into Paint. First, use the eyedropper (color pick) tool and click on any corner of the green rectangle. Select the eraser. With the eraser set to its largest size, wave the eraser over the image while holding down the right click button. Make sure you are holding down the right click button or you will be erasing the whole image.
Congratulations go to DSKG & TeamHorwich on being FTF! Way to Go!