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