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