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