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