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