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)(11,17)(12,15)(13,16)(14,20)(18,22)(19,23)(21,24)(26,31)(27,35)(29,33)(36,38) involution — undirected(2,3)(6,7)(9,11,15,13)(10,16,12,17)(14,19,22,21)(18,23,20,24)(25,26)(27,32)(28,33)(29,34)(30,31)(35,39)(36,37)(38,40)(1,2,5,3)(4,6,8,7)(10,12)(16,17)(18,20)(23,24)(27,35)(32,39)(36,38)(37,40)(1,3,5,2)(4,7,8,6)(9,12,15,10)(11,16,13,17)(14,20,22,18)(19,23,21,24)(25,27,30,35)(26,32,31,39)(28,38,34,36)(29,37,33,40)(1,4,5,8)(2,6,3,7)(9,13,15,11)(10,17,12,16)(14,21,22,19)(18,24,20,23)(25,28,30,34)(26,33,31,29)(27,36,35,38)(32,37,39,40)(9,14)(10,18)(11,19)(12,20)(13,21)(15,22)(16,23)(17,24)(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.