4. A method according to claim 3 , wherein said first set of colorable areas continues to be colored following exceedance of said at least one threshold.
4. A method according to claim 3 , wherein said first set of colorable areas continues to be colored following exceedance of said at least one threshold. 5. A method according to claim 4 , wherein colorable areas forming part of at least one of said first set of colorable areas and said second set of colorable areas become colored sequentially.