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