So from what I have observed in the movie, inverted people do not appear to be blind.

So we can presume light acts the same on eyes even when coming from an inverted source (compared to the person).

Furthermore, inverted lightsources in inverted places also seem to behave normally.

So if inverted light can be seen, and still follow other inverted rules, then we can use that to communicate with intelligent life in distant stars.

Here's how. You invert a powerful laser, or radio spectrum equivalent, whatever would be better.
You aim it at starsystems that might have intelligent life.
Say you have a good candidate 120 lightyears away, The laser sends a message. The inverted light travels backwards in time, and arrives at the starsystem 120 years ago.

Then, if there were aliens there 120 years ago, and they were capable of reiving a message, they might reply using an ordinary signal. 120 years later, in present day, contact is established.

If that happens, instant communication will be possible, all be it with the past.

And if the aliens have an equivalent to the theory of relativity, they would have their minds blown when they understand that the signal breaks light speed restrictions.