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