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