It's not Mark Rothko, but one can have an enormous amount of fun trying.

You will need:

• large sheets of watercolour paper
• a limited palette of watercolours - 2 to 4 (consider harmonious colours)
• large watercolour-suitable brushes

Do:

• Create multiple layers of transparent washes, allowing each layer to dry before adding the next.
• Make sure some of the layers overlap.

Notes:

• Use glazing techniques to build depth.
• Mix small amounts of pigment with a lot of water to increase the transparency.
• Use a wet-on-wet technique to create soft, feathery edges between colours.
• Vary the intensity and saturation of your colours to increase depth.