A person wearing a purple helmet is snowboarding down a hillside.
A person is wearing a blue hat.
Purple and blue are different colors.  A helmet is a specific type of hat to protect your head.  The person would have a purple helmet or a blue hat since you can only wear one hat at a time.
exists e1 e2 s1 s2 x1 x2 x3 x4.(a_down(s2) & Manner(e2,s2) & Theme(e2,x4) & Actor(e2,x1) & v_snowboard(e2) & n_hillside(x4) & Theme(e1,x3) & Actor(e1,x2) & v_wear(e1) & n_helmet(x3) & a_purple(s1) & Theme(s1,x3) & (x1 = x2) & n_person(x1))
exists e1 s1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_wear(e1) & n_hat(x2) & a_blue(s1) & Theme(s1,x2) & n_person(x1))