Outer space is a playground for scientific exploration, but it can be hard to visualize the data we capture. In most cases, images found in scholarly space articles like those from NASA are merely artist's renditions rather than pictures of the actual thing, and there's a good reason for it.
Space observation equipment can gather data, but it's not very good at zooming in far enough to snap a crystal-clear color photograph of an exoplanet. Most of the time, exoplanets look like small 'blips' or drops in starlight as they transit the host star, but chemical analyses can help scientists discern what type of exoplanet it is, be it gassy or terrestrial.
Artist renditions exist merely as a visual representation to complement public statements. Pictures are worth a thousand words, and they can help the public better understand a concept residing several light years away.
Creating these renditions is a delicate art, and artists must be careful not to be misleading in their imagery. In most cases, artists communicate closely with the scientists involved in a study to drum up the best possible visualization before publishing it.