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