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