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