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