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