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