A handy trick is to add some extra space to your canvas. Divide it into small squares with guides and fill each of the squares with a colour you want to use.

When in brush mode, holding down Alt gives you the euyedropper tool so you can choose your colour. Then let go and continue painting.
Choose your hues a bit apart and add a new layer for each one. That way you can easily fade it or rework it without touching the other layers.

There are no Borg. All resistance is fertile.