I've realized that the new mIRC inverts colors when you highlight text. I do have a slight problem with this because I have blue (12) text on a black background, and this produces a lovely eye-burning yellow text on white highlight. This isn't the main problem though. Let's say you decide to bring up the colors with ctrl + K and you do 0,0 for white text on a white background. The only way you can see that text is to copy and paste it again. Highlighting it will NOT uncover it like in previous mIRC versions.
While I think the inverting of colors was neat, it's not working quite well. I much prefer the older way where it simply reversed my colors (blue on black highlighted to black on blue was so much easier on the eyes, and I could highlight hidden text). mIRC 6.18 anyone?