I6: clearing the screen in RestoreColours() if COLOUR is set

[allensocket]

@DavidG

Can we get the ball rolling on examining this limitation in depth and what, if anything, can be done to alter the specs to allow for color changes of the sort that the Zmachine can do but Glulx can’t?

There was some very recent discussion on this topic here: [INFORM] The Reliques Of Tolti-Aph - right now we need an extension to output Glk calls?