I'm creating a booklet where only the first and the last page are allowed to be colour and the rest grayscale (for printing; CMYK). How do I do this with Scribus?
Just make separated files. One for the interiors and other for the covers.
The interiors should be nor printed as CMYK, but grayscale only.
An aditional tip: Depending on the pint system and the number of total booklets printed there is a chance you can actually have the interiors of the cover pages in full color too at the same price. Ask the printer.