I have a suggestion for ECM mode-you can change the primary color each char, and so even though you only have 64 chars in 4 bg colors, it would be helpful to be able to add more than 256 chars to the palette in ECM mode, as long as it matches one of the 256 defined chars. Great software! Thanks so much!
I'm glad you found a way :)
To be honest I am still unclear quite what you were trying to do or why, but I know everyone just needs what they need for their own project.
Another common way of having the same char in different (matrix) colours without having to duplicate them is to create a 1x1 tile-set and use per-tile colouring.