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