This is part of a blog post I added a couple of years ago to my main blog (www.studiohyde.blogspot.co.uk), but I thought it would be helpful here too.
Warm and Cool tones in paintings.
My example is this sketch of Barnstaple bridge.
Pen + watercolour
plus I added a small amount of detail with
my Sailor Calligraphy pen
Note: The majority of this painting is in cool tones:
So to balance that out I added the warm red stripe on the boat.
Equally, if a painting is mainly warm tones,
then offset it with some COOL colours
It all helps the BALANCE of a painting.