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