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