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