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