San Francisco, May 17 : Apple is reportedly testing the use of a colour display from E Ink as an external screen for an unannounced foldable device. Analyst Ming-Chi Kuo said that the tech giant is testing E Ink's Electronic Paper Display (EPD) for future foldable device's cover screen and tablet-like applications. "The colour EPD has the potential to become a mainstream solution for foldable devices' must-have cover/ second screen thanks to its excellent power-saving," the analyst wrote in a tweet. According to The Verge, most tablet-style foldables on the market pair a large folding inner display with a smaller outer display for quickly checking notifications. But existing devices like the Samsung Galaxy Z Fold 3 or the Oppo Find N use OLED panels for both. Apple's use of an E Ink screen would almost certainly make for a less responsive outer display with fewer colours but, as Kuo notes, it could be far more power-efficient, the report said. Although E Ink is best known for its monochrome displays that Amazon uses in its Kindles, the company also has a line of colour screens, it added. Most recently it announced E Ink Gallery 3, a new version of its colour E Ink technology that's capable of producing more colours at a higher resolution. It can also refresh far quicker than the company's previous colour screens, although it's still nowhere near as responsive as an equivalent OLED or LCD panel. /IANS