The color '...' is not recognized.

[akim-13]

I have a color scheme set up on my laptop in the following way:

# Colors
color=1
rule.precedence.color=overdue,uda,deleted,completed,active,keyword.,tag.,project.,scheduled,due.today,due,blocked,blocking,recurring,tagged

## This is a theme that disables all default colors.
## It can be used as template for other themes.
include /usr/share/doc/task/rc/dark-256.theme

color.active=black on rgb141
color.blocked=black on color8
color.due.today=on inverse
...

It works fine. However, recently I tried using taskwarrior on Termux (terminal emulator for Android) and with the same setup I get this error: The color 'black on rgb141' is not recognized., even though when I run task color black on rgb141 it gives the expected output. Why might this be the case?

Idc too much about setting colors in this particular way, so if there is another more robust way to specify them, I might as well try it.