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