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