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