I think, this is not impossible to achieve.
I know it is not, I am doing it albeit a bit less "elegant" than the proposed chip using 3 of the ST2221A http://www.siti.com.tw/product/s...T2221A.pdf chips, one for each color. Also to use these chips I have to upload separately for each weight.

Just interested, what is the planned thermal dissipation of the chip (what kind of package)?
I do not recall, but in the last meeting was stated "we will use package xxx it's gerat for dissapation.

You undoubtly considered multiple voltage power rails for the different colour LEDs...
That would be ridiculous when employing costant current circuits the only effect of the volatge is dissapation, thus I use 3V3 for Amber and 4V for color.

Erik