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