I have been asked to clarify "effective". "I have an alien contact concept running where they are telepathic. Right now I have imagery being sent mind to mind, but the only thing I can think of is that this could be misinterpreted as aggression, given how xenophobic the world's governments seem to be. How else might they communicate effectively? TIA..."
Let's say an alien race wants to make first contact with inhabitants of earth. Peacefully, no aggression. They communicate primarily through telepathy, although color changes and gestures can enhance or modify what ever is being sent telepathically. I'm using imagery, but I'm guessing other cues like smell and what's being sensed through other physical input could be transmitted/received as well telepathically.
Humans are verbal, and for decades have been dumping radio waves into space in many, many languages. So, other than the proverbial "We come in peace" statement from '50s B movies, it's not clear the languages could be deciphered on their end.
I'm assuming face to face contact, or even physical contact. "Effective" here means little ambiguity on the peaceful/aggressive scale. Does that help at all?