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