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