The problem is most likely in this part (no pun intended):
/part # %partm $+ $colour(part text) $+ |
%partm is probably empty, so all is left is the value of $color(), which is probably 10 in your case. I'm not sure why you need $color(part) in your part message so the whole thing looks wrong, unless %partm is supposed to end in a Ctrl+K character. Also, "$color(part text) $+ | ..." is invalid (even though mirc doesn't complain): it makes no sense to concatenate $color() with, well, nothing. If you don't want anything to follow $color(), just remove that $+ from there.
