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