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