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