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