From your Board, start by adding a shape.
1 - Add a shape
In your toolbar, click on "add", then on "shapes".
Select a shape with a single click.
By default, it appears with a black outline and a white background.
2 - Change contour color
To change the outline color, select the shape and click on the 2nd icon in the editing bar.
Then select a color.
3 - Change fill color
To change the fill color, select the shape and click on the 3rd icon in the editing bar.
Then select a color.
If you'd like to add color to your palett, discover all the color options in Board: Board color selector