Every video chipset has a pre-defined palette and colours displayable.
Its all digital. The ST's was limited to 16 displayable from 512/4096
(ST/STE), TT's was 256 displayable from 4096 and Falcon's was 65,536
displayable from 262,144. I think the 320x200 res's were limited to 16
colour on all the machines. The Falcon has a 320x240 mode that is VERY
compatible given the right software. This res can display 65,536 colours
(Falcon truecolour) as well.
The display isn't hackable/configurable in a simple sense. There was a
shifter mod that added a second shifter to an ST/STF/STM/STFM and gave
it a palette of 4096 but apart from that I don't think anyone bothered.
There were a few video card options kicking around, mostly fro the
Mega's and the TT.
Also there were some programs that use a technique called palette
switching. This can fool the machine into displaying its entire palette.
I.e. 512 colours on an ST. This cannot be done from GEM/TOS AFIK. Thru
trickery it is possible to shoehorn 19000 colours out of an STE. Another
thing too, this switching technique is very CPU intensive, most of what
I've seen has been done in assembly. Have a look at a program called
Photochrome for the ST/STE.
Depends how it was written I would guess. Hard to say.
Good luck ;-)