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