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