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