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