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