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