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