Colour
The palettes for your chosen colours are located on the bottom right of the application window. By default there are 10 palettes available:

Clicking on the buttons that have the labels "Palette 1", "Palette 2" etc. will make that palette the current palette.
Once you have selected a palette to use, click on the "Colour" button on the right of the application window:

This will open up the Colour Chooser window, and you can choose a colour by entering the red, green, blue values or by pressing the = and - keys on your keyboard to change the values. For example, to enter a value of 100 for red, I can type in "1" "0" "0" or I can press "=" 10 times. Then to enter a value for the green component, I press "g" on my keyboard to enter a green value, and I can either type in a number of 000 to 255 inclusive or I can adjust the value by +- 10 by using the "=" and "-" keys respectively. It is similar for the blue component, where I start by pressing "b":

The previous colour of the palette is the left block of colour and the chosen colour is the right block of colour.
Then click "Confirm" to assign the chosen colour to the selected palette. Pressing "Cancel" will close the Colour Chooser dialog without changing the colour of the palette. In other words, it will remain the left block of colour.
We can see that the chosen colour is now assigned to Palette 1, and can be used by clicking on the Palette 1 button:
