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