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)(12,17,28,34,27,35,26,33)(22,36,38,30,25,39,37,40)(9,11,13,23,14,24,15,29)(10,16,19,21,20,32,18,31)(12,25,26,38,27,22,28,37)(17,30,34,39,35,40,33,36)(1,3)(2,6)(4,8)(5,7)(9,12,14,27)(10,17,20,35)(11,22,24,25)(13,28,15,26)(16,30,32,40)(18,34,19,33)(21,36,31,39)(23,38,29,37)(1,4,6,5)(2,7,3,8)(9,13,14,15)(10,18,20,19)(11,23,24,29)(12,26,27,28)(16,31,32,21)(17,33,35,34)(22,37,25,38)(30,36,40,39)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.