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