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