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