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Basic Procedure
Take images in each band such as L, Red, Green, Blue or H-Alpha, O-III, or SII. Collect Darks, Flats, Lights, and Biases one at a time. Note that you will only need one master set of Darks and Biases since they are taken in the dark and are not dependent on the filter used.
Each color or narrow band should be in their own folder within the master directory for the project. These bands and individual channels will be stacked to form a master for each channel.
Open up Siril and process each color or narrow band one at a time using the monochrome script. Save the image from each band in the master folder with good naming such as red_stacked, blue_stacked etc.
Combine Monochrome Images To Form A Color Image
Now that each color or filter band is saved, the next step is to align the images. This procedure is called Registration.
Add all of the channels in the Conversion tab and press “Convert”. Next align the images with the Registration tab. Do not stack.
Now go back to Image Processing->RGB Compositing. Here you can assign R, G, B, L, or any narrow band image to combine into a single color image. Select them from the list. Note that the numbering order may be different than RGB. It might be BGR so select accordingly.
A preview will now show and you can color correct at this point. You can open one of the color tabs and select a dark area. Draw a box around the dark area and choose “Use Current Selection”. Then click “Background Neutralization”. Now check the RGB tab and see if the preview better reflects the color you would expect.
Export Or Further Process
At this point you can save a Tiff of the linear version for further processing in Gimp or Photoshop. You could also use Siril’s image processing if you choose.