So you have a few colours in your collection, most of us have. Some colours may be missing like SEPIA or VANDYKE BROWN, even BURNT UMBER.
Well, if you have Raw Umber, Ultramarine Blue and Burnt Sienna....these will give you those missing colours.
RAW UMBER + ULTRAMARINE BLUE = SEPIA
SEPIA + BURNT SIENNA = VANDYKE BROWN
RAW UMBER + BURNT SIENNA = BURNT UMBER
Go on, give this a try and see the outcome,
so easy to add to your collection of paints this way.