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