COLOUR TRIADS
TRIADS, not the far eastern mafia but three colours.
When you have lots of colours it can get confusing , some artists like to see what they can do with three colours (plus black and white if needed, (not always needed, you can usually mix a black wiht your triad choices, and  white is not needed  in watercolour)
a basic triad would be Ultramarine, lemon yellow and alizarin crimson .
Try it on a simple picture this, or one of your own.

You could change it by just changing one colour, replace ultramarine with prussian blue or Phthalo blue, replace the red or the yellow.

Other triads
a very bright one: phthalo blue, lemon yellow, permanent rose
a deep earthy one: Prussian blue, crimson and yellow ochre.
A dark one:  Paynes grey, crimson, burnt sienna.
You can combine any 3,
An unusual one: Black, cadmium red, cadmium yellow

Experiment and enjoy your colours, if you get a result you especially like repeat! or you will not learn. Repeat repeat!