"it also works for brightness and contrast" If all the values add up to 99 or 100 it will not change the brightness. If you use more of one colour compensate by reducing the amount of another eg. if you want a sky where the clouds show up more against patches of blue sky use more red. If you wanted to lighten the colour of foliage use more green but retain the total as 100. Brightness can be tweaked in levels or however you would normally do it after.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html