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