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