Clicking on the Kes 75 supernova remnant below will load three energy cuts of a single Chandra observation. Because these three images have the same size, scale, and pointing direction, you can assign them the red, green, or blue colormaps. Then, if you then select the menu option Color->rgbMode, they will be displayed as one RGB composite image.
In RGB mode, the current image (as shown in the File menu) still determines which of the three independent colormaps is changed by contrast/bias mouse manipulation, available for data analysis, etc. To remove an image from the RGB composite, give it a different colormap. Re-join (or add a new image) by assigning one of the RGB colormaps. Turn off rgbMode to display the images separately.
Clicking the Orion Nebula below will load three images with the same size and scale, but slightly different pointing directions. Thus, when you display them in RGB mode, the images will be slightly offset from one another. To perform a manual alignment, use the arrow keys that are displayed with Orion. Pressing a key will call the JS9.ShiftData() public routine to shift the image (as well as its underlying data) up, down, left, or right.