In reality it was a gradual thing that kind of crept up over time. I said technically earlier because Desi Arnaz is "Technically" white, idk who decides where these lines are drawn, it's definitely not me lol. William Shatner(cause that's how he rolls I guess) also kissed actress France Nuyen (half white/half Chinese) on TV, which could also be considered first.

The kiss between Shatner and Nichols is the first kiss between a white and black person on TV. Which if you're a racist would probably upset you the most so it gets mentioned as the first I guess.