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