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