In that case you can either re-install mIRC and select it to install settings (which will overwrite all your existing settings and you'll have to reload any scripts again) or you can do the following which is a bit more complicated but should leave all your settings and scripts intact:

1. Type //run $nofile($mircini) in mIRC to bring up the folder containing your mirc.ini (the file containing mIRC's settings).

2. Close mIRC.

3. Create a copy of mirc.ini (in case anything goes wrong)

4. Open mirc.ini in a text editor and find a line that just says "[colors]". From what you've said there should be another line directly beneath it that begins "n0=mIRC Classic" followed by a lot of numbers and commas.

Insert the following text into the lines below that "mIRC Classic" line:
Code:
n1=mIRC Modern,0,6,4,7,2,3,4,3,3,3,3,1,5,2,6,1,14,2,3,5,1,0,1,0,1,14,5,0
n2=Monochrome State,1,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,15,1,15,1,15,15,15,14,1,15
n3=Placid Hues,0,2,4,7,2,3,3,3,3,15,3,1,5,7,6,1,3,2,3,5,1,0,1,0,1,15,6,0
n4=Rainbow Sky,0,7,4,5,1,1,3,3,8,13,3,14,2,7,13,5,3,8,3,4,14,0,5,0,3,14,10,0


5. Save the file and restart mIRC. If all goes well you should now be able to select the colour scheme you want from the dropdown list. If it doesn't work for some reason you can close mIRC and use your backup mirc.ini to get back where you started.

Spelling mistakes, grammatical errors, and stupid comments are intentional.