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