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