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