What OS are you running? Maybe this is an issue with mIRC initialising an integer at a weirdish number on some systems (Khaled is using a new compiler after all). Although it's kind of bizzare that it only effects colour 16 and none of the other 'vacant' colours, and that it only seems to be one colour (two if you count the 24 and 16 bit display difference pointed out above) and not a diverse range of colours one would expect given different systems configurations. To the technically savvy: when a variable is initialised with 'garbage' is it the same garbage all the time?
Maybe this is an easter egg?