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