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