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