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