Is it possible to add your own colours to the colour picker. If so how do you do so?
Down in the Standard Colors section you can add more colors by including styles like this:
Similar you can define new background colors using .ms-rteBakcColor-XX
The colors at the top are controlled by the theme and should not be modified by CSS
You can change these colors by creating a .spcolor file.
I think the colors you need to change are :
You can start from a standard .spcolor file located in "/_catalogs/theme/15".
Hope this helps