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