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