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)(11,17)(12,19)(15,20)(16,23)(21,22)(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)(9,10,12,14,13,15,19,20)(11,16,18,21,17,22,24,23)(26,30)(27,34)(32,33)(35,40)(2,6)(5,8)(10,15)(11,17)(14,20)(18,24)(25,27,28,34)(26,31,30,37)(29,35,36,40)(32,38,33,39)(9,11,12,18,13,17,19,24)(10,16,14,21,15,22,20,23)(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.