16 colour EGA palette with dithering

Hi guys,
Looking to use Aseprite to do some background in 16 colours. I was using SciStudio’s drawing tool which uses a palette like this made up of 16 colours (MSDOS EGA) as a base then additional colours mixed with another colour:

Is there a way to add to the existing CGA palette the “dithering” colours (ie one of the 16 colours mixed with another) so they appear in the palette on the top left?