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