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