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