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