One vertex per element, one color per generator, with an edge from x to x·s.
(1,2,4,7,5,8,3,6)(9,10,15,20,16,21,14,19)(11,22,18,33,25,13,30,23)(12,26,28,35,29,37,32,17)(24,39,34,27,40,38,36,31)(2,6,8,7)(9,11,23,10,16,25,33,21)(12,24,38,17,29,40,39,35)(13,19,14,30,22,20,15,18)(26,28,34,27,37,32,36,31)(9,12,15,32,16,29,14,28)(10,17,19,26,21,35,20,37)(11,24,18,36,25,40,30,34)(13,31,33,39,22,27,23,38)A Cayley diagram is a choice, not a fact about the group. Another drawing of this group — in a book, or on a different generating set — may look nothing like this one.