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