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