Color control is done by having many extra I/O pins available and having more code space by using a more advanced MCU, the 1634, see the Atmel family of MCU's here: https://en.wikipedia.org/wiki/ATtiny_microcontroller_comparison_chart
NarsilM and Anduril previously required the ATtiny85, first came out in 2005, then TK added supported for the 1634 (and possibly other variants). The 1634 first came out in 2011.
Our goal should be, maybe is right now, to support the ATtiny1616 or ATtiny3216 (out in 2018) because mainly of the feature listed in the far right column: UPDI, plus they have 16 KB and 32 KB of code space (ATtiny85 has 8 KB). UPDI allows 1 pin flashing. The advantages of UPDI have been discussed here in the tech threads, but maybe not a 1 pin, but I think 3 pins can be used for a pogo pin flash kit.
Our ideal MCU right now would be a 20 pin flat pack (called QFN-20 in the chart), and having UPDI. The 4 mm x 4 mm size is nice and compact for our drivers, and relatviely easy to design in. The "1-series" MCU's on the chart are preferred. See gchart's thread: https://budgetlightforum.com/t/-/55911