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