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