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