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