You have a nice keyboard shortcuts currently, that 1-2-3-4 and b-g-r-w-d for coloring. Seems like it really speeds up working with a tool.
May I hope that picked custom colors would be available the similar way? Like, q-w-e-r-t-y buttons are not binded yet for example.

P.S. Calculating font colors automatically seems pretty viable, color picker looks good, unless you have to dive into it for each note - mouse clicks and menu diving are much more time-expensive than keyboard shortcuts you have.

i'll have to think about that , i like the shapes being associated with the finger numbers

Like that as well. c-d-t-s are scattered all around the place, harder to reach physically. It's also not that natural to remember for a non-native English speaker, compared to just finger numbers. Not like completely unsolvable, but took some time for me to guess why this particular letters are mentioned.
(And I still do not know why "d" is for black color, by the way, I would rather expect K as in "CMYK" )

Probably that's the reason why I'd suggested moving colors to qwerty, as I do not feel any pronounced relation between colors and first color name letters anyway.

ok i added the color picker menu/dialog

keys <shift>1 through <shift>9 now let you select color 1 - 9 from the custom colors you save in the dialog 1 is the latest color you saved 2 is the second latest and so on...

i also changed the key for black to be 'k' instead of 'd' per your suggestion

Note i have not put the contrasting text calculator yet ( i forgot about it i'll probabaly get that in tomorrow
i think with this scheme you can just pick the 9 most used colors you are working with at the moment and then just use <shift>1-9 to color your position dots with the keyboard.
and that will cover 99% of the keyboard color selection acceleration needs you may have i think

Looks like color picker keeps custom colors configuration in cookies between sessions. Even convenient, and you still can clean the browser site cookies to reset the saved colors.