Well, there has been a distinction in the past between the 2 types of herpes simplex virus as an oral strain and as a genital strain. However, over time, with more people enjoying oral sex more often, and as a general rule, with more partners over their lifetimes, the distinction line has blurred or even disappeared. It is possible to have "genital" herpes virus orally, and "oral" herpes virus genitally. However, the general guideline for both places is to avoid contact while you are having an outbreak, or if you feel you are going to have an outbreak. Even though the virus can be spread when there is no sore visible, it is much less likely to happen. There are also products available at your local drug or larger grocery store that can shorten the duration of an outbreak.
Enough mumbo jumbo... the best way to avoid transmitting your oral herpes to your partners genital area is to use protection. But, if you don't use protection, certainly don't do oral while either of you has a cold sore!!!