Selling your textbooks is a great way to make a little extra coin at the end of a semester. And the more mint your copy is, the higher the price you can usually pull from it. Unfortunately, your need to highlight important parts of your textbooks to ease studying makes "mint condition" a far-flung pipe dream. Not if you use the Fader, a fading highlight marker.
The good news? That's a whole lot of awesome. The bad news? It's currently still just a proposed project at Quirky. The technology should be readily available, as we've seen many products use disappearing ink in the past. A fading highlighter makes perfect sense, though, so we're hoping it does push through as an actual product.
With the Fader, you can mark your books the way you've always done, highlighting every passage or fact that you want to pay extra attention to. The yellow colored markings will stay on for later reference, gradually lightening until it fully disappears after five months. Do note that there's no way to hasten the ink's disappearance, so don't go marking books you borrow from classmates unless you want a beef on your hands.
The actual marker looks like a standard highlighter, measuring 150 x 17.25 x 13 mm. It features a plastic body and plastic lid, with a brushed metal clip on the non-writing end. Of course, this is the early prototype design, so it can totally look like something else by the time production rolls around. Either way, the disappearing ink is the main selling point, so it's not that big a deal.
You can check out the Fader's project page over at Quirky.