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