Green’s Dictionary of Slang

(US black) a white racist bigot.

1968		‘Sl. of Watts’ in Current Sl. III:2 52: Yakoo, n. Caucasian.
1972		D. Dalby ‘African Element in American English’ in Kochman Rappin’ and Stylin’ Out 185: yacoo — ‘white racist.’.
1980		E. Folb Runnin’ Down Some Lines 60: Young blacks, particularly ghetto blacks, have very accurately and clearly ‘seen’ whites for what they are perceived to be in the black community. They are evil (devil, yacoo) [...] and above all they are people of no color, no soul.