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