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