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