That's because Kepler-186f orbits a red star, and we're just speculating that perhaps the plants there, if there is vegetation that does photosynthesis, it has different pigments and looks red.
To je zato jer Kepler-186f  orbitira oko crvene zvijezde te pretpostavljamo da biljke ondje, ukoliko ima vegetacije  koja provodi fotosintezu, imaju drugačije pigmente pa su crvene.