In the older days where terminals originate, they were hardware, and their colourfulness was limited by hardware constraints (i.e. memory shortage). Now we mostly use virtual terminals, which often emulate these older devices in software. So, one point is whether the software terminal actually emulates a device with its historical limitations.
Another point is that there are no conceptual limitations on colours, fonts or anything. This is because terminal is controlled by commands, which are simply special reserved sequences of characters. Commands are not standardized and differ from a terminal to a terminal. And that’s exactly why there are virtually no such exotic functions implemented, as it would leave the users with two limiting options:
- require all terminals to support the feature (which is not practically feasible)
- limit the usage of the software to few particular terminals which do support the feature (which is highly unpleasant).
The third point I’d notice is that such features are not really needed by majority of people.