The first interracial kiss happened in a color mainstream comic called Amazing Adventures Featuring Killraven published by Marvel Comics. Killraven was a freedom fighter in an apocalyptic future Earth in which martians had invaded and taken over. Killraven led a group of free humans to fight off the martians.
Well in Amazing Adventures #31 (1975), written by Don McGregor with art by P. Craig Russell, the first interracial kiss happened between two of Amazing Adventure's supporting characters. M’Shulla Scott, the black character, was Killraven’s closest friends and Carmilla Frost was a white scientist.
It’s also noteworthy that Don McGregor accidentally wrote the first interracial kiss in mainstream black & white comics which happened in Warren Publishing’s Creepy #43 in 1972, 3 years earlier. It was the result of miss-communication between McGregor and the artist Luis Garcia.