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