When you double click in the room for the room properties you can change the topic. When you change colors in this edit line you can use ctrl k to make the colorwindow popup. Clicking a number in this window will not cause the chosen number being added to your line, but it will select your entire topic

This bug was reported in 6.16 and is still present in 6.17
https://forums.mirc.com/s...SID=#Post150166

Thanks this has been fixed for the next bugfix release.