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