color(A,B,C,D,E):-next(A,B),
                  next(C,D),
                  next(A,C),
                  next(A,D),
                  next(B,C),
                  next(B,E),
                  next(C,E),
                  next(D,E).

next(X,Y):-selectcolor(X),selectcolor(Y), X \== Y.

selectcolor(red).
selectcolor(green).
selectcolor(blue).
selectcolor(yellow).