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