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