Do you mean when you copy text from message windows or from logs? If you're copying from windows it shouldn't copy the color codes too. Just the text. If you want to disable codes, go to Options (Alt+O), IRC, Messages and under "Strip code from incoming messages" check Bold, Underline, Color and Reverse.
If you want to strip them from logs go to Options (Alt+O), IRC, Logging and check "Strip codes".