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