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