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