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