The original color specification
There have been a wide range of suggestions for how to add more color support and you can find what others have suggested if you search this forum. Any of the suggestions would require a fair amount of work and doing something only part-way such as adding a few extra local colors really wouldn't be the best way to handle it. If more colors are going to be added, it would be far better to do it right and provide a decent number of colors or options to use RGB or something else. Otherwise you end up with basically what you have now, but with a few extra colors instead of providing the ability to truly customize your colors as much as you want.
had more colors. But mIRC ignored it and used the EGA palette instead. OOPs. I don't think mIRC will ever see more colors.