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