Lots of differing opinions among cartoonists about whether daily comic strips should be colored.
The cartoonist gets paid no more for the extra work. If they want any control over how their work looks, they take on the extra work anyway.
Reed-Brennan, the main proponent of colored dailies, used to advertise that color sells more papers... until Rick Kirkman (Baby Blues) called them on it and they had no evidence for the claim. R-B does charge newspapers extra for colorized dailies, though... a hundred dollars a page or so.