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