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