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