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