Bluelight treatment on glasses refers to a filter applied to the lens of the glass. You can sometimes detect a slight blue reflection from the lens and an overall yellowness of the lens. The filter is designed to cut out the blue end of the visible and ultra-violet light spectrum. You might notice that whites appear slightly yellow, but otherwise colour perception is quite unaffected.
It is thought that the increased use of screens which emit bluelight (computers, phones, tablets, TVs, etc) can upset normal sleep and rest patterns. Especially so late at night, immediately before sleep. Whether it is the bluelight or the focus on a screen for large parts of the day and just before sleep is unclear. Anecdotally, many people feel that the bluelight filter makes their eyes feel more rested after a day of screens.
So far, there is no scientific evidence to back this up, or to separate the effect of the wavelength versus the extensive use of screens. In the mentime, they look cool and there is no harm in potentially protecting young eyes.