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