If the assignment is for you to come up with your own slogan, I might suggest examining some of the Civil Rights Movements' slogans of the time. I think that these might be good for you because they help to capture a moment in time, a consciousness, a feeling of what racial harmony was meant to be. Examining those statements might be a good start. For example, I like the slogan chanted and sung often in song, "We Shall Overcome." What three words better capture a mood, a feeling, an experience of attempting to overcome racial discrimination and achieve racial harmony. Another good place would be the music of that time period, completely influenced in many ways by the experience of the Civil Rights Movement. Sam Cooke's song, "A Change is Gonna Come" is a wonderful slogan to capture the progressive and optimistic tone that is present in the Civil Rights Movement. I have always been partial to Sly and the Family Stone. I love the ending to the song, "Everyday People: "I am everyday people." I think that you might have to reflect on what it is you want to go ahead and say about racial harmony and then be able to articulate what you want to say in a slogan, something capturing the essence of your feelings about it.