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