A crowd of people are walking, they are mostly dressed in white.
Some people dressed mostly in white, are walking.
A crowd of people can also be described simply as 'some people'. 'people dressed mostly in white are walking' is a rephrasing of 'people are walking, they are mostly dressed in white'.
exists e2 e1 s1 s2 x1 x2 x3.(a_mostly(s2) & Manner(e2,s2) & Theme(e2,s1) & Theme(s1,x3) & a_white(s1) & Theme(e2,x1) & v_dress(e2) & n_thing(x1) & Actor(e1,x1) & v_walk(e1) & of(x1,x2) & n_people(x2) & n_crowd(x1))
exists e1 e2 s1 s2 x1 x2.(Actor(e2,x1) & v_walk(e2) & in(e1,s2) & Theme(s2,x2) & a_white(s2) & a_mostly(s1) & Manner(e1,s1) & Theme(e1,x2) & v_dress(e1) & (x1 = x2) & n_people(x1))