|Step 3: For each image, go to Process > Color Tables, and select the color that is appropriate for each image. To see which image was taken with which filter, go to Window > FITS header.
Step 4: Go to Process > Shift. For the easiest shifting, select the green image as the background. Then, select one of the 2 other images for the first foreground. Use the mouse to drag the foreground image until it matches up with the background image. Then, select the last color and match it to the background image. When you’re done lining up all 3 images, click OK.