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