Choosing colours

To mix nice clean and vibrant colours from red, yellow and blue you will need to have one each of a cool colour and one of a warm colour.

A cool yellow will look a bit greeny and Lemon Yellow is a good choice
A warm yellow will look a bit orangey and Cadmium Yellow is a good choice
A cool red will look a bit purpley and Permanent Rose is a good choice
A warm red will look a bit orangey and Cadmium Red could work for this
A cool blue will look like the sea, a bit green. Windsor blue (green shade) or Turquoise
A warm blue will have a bit of red in it. French Ultramarine is a good colour.

Try mixing two colours together to see if it makes a nice clean sharp colour or a muddy colour. It depends on whether your mix contains only two of the primary colours red, yellow or blue.

eg.

Cool Yellow + Cool Blue = vivid acid green
Warm Yellow + Cool Blue = muddy green
Cool Yellow + Warm Blue = muddy green

The muddy green comes when there is a bit of the third colour in the mix somewhere ie the red. The red would be present in a warm blue or a warm yellow. And if you mix the 3 primaries together you start to get browny black.

Warm Red + Warm Yellow = vibrant orange
because there is no blue in any of the paints. a cool red has a touch of blue in it and a cool yellow has a touch of blue in it.

A Cool Red and a Warm Blue = Vibrant Purple as both of these colours have a touch of blue or a touch of red but no yellow anywhere.

Look up on the internet about colour wheels and start to learn how colours work together.