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