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