By own fonts and own color scheme, I meant allowing each user to customize their own TIC.
Like a tiny config file that change the default color palette on boot up (but keeping the 16 colors limitation).
As for the font, a special directory where you can place your custom font so it gets loaded on boot up.
But the font and the color scheme wouldn't be stored in the cartridges (well you can still change the color scheme by playing with the RAM). It would be just a setting for this particular user.