It seems that it's not a matter of the window focus changing, but when mirc redraws the text. For example, selecting and deselecting the line does it. Moving another window on top of the text also does it. In one test, I moved my status window so that it covered the bottom half the text in the listbox, and only the bit that was covered over got changed red -- a strange sight indeed! Changing window focus itself has nothing to do with it, as long as the text is not hidden, or the window resized. Seems that the root of the delay is that mIRC changes the text color in memory, but skips the part where it redraws it on screen.
