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