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