"Love. It Comes in All Colors." was part of the National Urban Coalition's campaign to promote "racial" harmony. Political activists and celebrities from different fields participated in the TV commercial and print advertisement produced in 1970. The commercial showed a group singing "Let The Sun Shine In" and was broadcast during shows, for instance "The Ed Sullivan Show" (via).
Among the many celebrities was ... just have a look: third row down from the top, far left ... yes, ... Leonard Nimoy.
Here the clip (Leonard is in at :30 and at :35):