No laser of which ever color is within what we use -— think outside the box as in fields instead of vectors to describe a comm system. cf James Clerk Maxwell (now obscure, but was greatest physicist after Newton and before Albert Einstein) — quaternions was the term he used to describe his fields, but 4 were rewritten as vectors and the other 196 were discarded, from the four comes the entire description of our EM spectrum. Aliens might use the other 196 of which we know nothing.
How about as modulated neutrino or gravitational wave emissions. These would have the advantage of being essentially immune to interference by intervening matter, but are very difficult to generate or detect with current technology.