or a new cmd to change colours?
Shake.screen(xxx) is quite good because...it's a standard?

Well, I wouldn't mind if interpreters would try to use even some common commands, like shake.screen for palette-changing, because incase one wishes to distribute both windows and dos-interpreters (E.g. nagi & agi mouse) with his/her game, one doesn't have to create two or more different versions.
And yes, I'm bit narrowminded, but still I wouldn't except too many games using shake.screen (in it's original purpose) with values greater than 100. So this command wouldn't probably harm game making like e.g. mouse-support which has taken push.script-command for it's ungodly purposes.
Anyway, like Chris said, I think also that support for the original function of shake.screen is feature with high priority.