One vertex per element, one color per generator, with an edge from x to x·s.
(2,4)(6,8)(9,10)(11,21)(12,26)(13,20)(14,19)(15,18)(16,23)(17,29)(22,37)(24,32)(25,33)(27,34)(28,35)(30,36)(31,39)(38,40) involution — undirected(1,2,3,4)(9,11,13,23,15,25,14,24)(10,16,19,21,18,32,20,33)(12,27,28,22,30,38,29,39)(17,34,36,31,35,40,26,37)(9,12,13,29,15,30,14,28)(10,17,19,26,18,35,20,36)(11,22,23,27,25,39,24,38)(16,31,21,34,32,37,33,40)(5,6,7,8)(10,18)(16,32)(17,35)(19,20)(21,33)(26,36)(31,37)(34,40)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.