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)(11,18)(12,17)(13,21)(14,16)(15,19)(20,24)(22,23)(26,30,32,35)(27,33)(31,38,39,37)(34,40)(1,3)(2,6)(4,8)(5,7)(9,11)(10,15)(12,19)(13,22)(14,20)(16,23)(17,24)(18,21)(25,26)(27,31)(28,35)(29,32)(30,36)(33,39)(34,38)(37,40) involution — undirected(1,4,6,5)(2,7,3,8)(10,16)(15,23)(17,21)(18,24)(25,27,29,33)(26,31,32,39)(28,34,36,40)(30,37,35,38)(9,12,14,13)(10,17,16,21)(11,19,20,22)(15,24,23,18)(27,33)(31,39)(34,40)(37,38)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.