3/2 - Approximation probabilistic algorithm for MAX-3-COLOR
If you simply uniformly at random (i.i.d) color each of the vertices of $V$ by each of the three possible colors, then for every edge $e\in E$, it's endpoint will be colored by different colors w.p. $\frac{2}{3}$, hence the expected quality of the random coloring is exactly $\frac{2|E|}{3}$. We know that the optimal quality is at most $q^*\leq |E|$, hence this is a $\frac{3}{2}$ approximation.