less or sass and colour schemes

Taking a look at these css pre-processors. What I want to do is to be
able to create and switch colour schemes easily. afaict I can easily
create variables for the different colours I use in a scheme, or rather
for the different places I use colours, so I would have say

primary-background-color
footer-background-color
header-background-color
primary-text-color
heading-text-color
footer-text-color
menu-text-color

But I can't for the moment see how I then save the set of variables as a...

less or sass and colour schemes