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