High-performance CCD cameras are fundamentally monochrome imagers. To obtain color images requires filters. Typically three or more filters are loaded into a filter wheel in front of the camera.
There are several ways to create color images. The most straightforward is to use Red, Green, and Blue (RGB) filters. In this case, assembling the color image is simple, since color images on a computer are normally stored with RGB color planes.
Often a separate Luminance (clear) filter is added to the mix; see Adding Luminance for more information. Sometimes imagers use CMY filters instead. The advantages claimed include higher signal-to-noise ratio; however, in reality after processing to RGB space for computer display the SNR improvements are tiny. The greater difficulty in achieving good color balance with CMY means this technique is generally inferior to RGB imaging.
Once the frames are acquired, they need to be combined into the final color image. The Stack command can do this automatically, as part of the stacking process. The Combine Color command does the same thing with individual frames.
The Color Stack allows you to stack an arbitrary number of filtered images together, and assign each a unique color. This can be useful in creating ”false color” images, or in integrating additional filter channels, such as Hydrogen-Alpha.