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