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)(12,16)(13,26)(14,17)(15,22)(18,27)(20,33)(21,29)(23,32)(24,37)(25,30)(28,35)(31,38)(34,39)(36,40) involution — undirected(9,11,14,23)(10,15,17,29)(12,20,25,36)(13,21,27,22)(16,28,30,39)(18,32,26,19)(24,34,38,35)(31,40,37,33)(1,2)(3,6)(4,8)(5,7)(9,12,14,25)(10,16,17,30)(11,20,23,36)(13,24,27,38)(15,28,29,39)(18,31,26,37)(19,33,32,40)(21,34,22,35)(10,17)(11,21)(13,27)(15,19)(16,30)(20,34)(22,23)(24,38)(28,33)(29,32)(35,36)(39,40) involution — undirected(1,3,5,4)(2,6,7,8)(10,17)(15,29)(16,30)(18,26)(19,32)(28,39)(31,37)(33,40)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.