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