Draw your shape in any colour and leave it selected / open the Gradient-Tab
and choose Linear (or Radial).
Click one of the markers left or right and choose your colour.
To create new ones just click below the gradient-line.
In the Toolbar activate the Gradient-Tool (G) and draw any line
in your shape to change the gradient position or put the number
into the Angle-window and hit return.
Cheers
Nolan