The new Fire HDX 8.9 now features Dynamic Light Control, which changes the white point of the display, matching its colour and warmth to the ambient light of your surroundings in order to make the display more closely resemble a piece of paper—this makes the best reading experience on a tablet even better.
The Fire HDX 8.9 also featured dynamic image contrast that according to Amazon, "automatically optimises the color of each pixel based on the amount of light in your surroundings".
All these devices, including the Kindle Voyage, as noted, were announced late 2014 in a designated hardware event. Amazon no longer hosts events to announce the release of Fire tablets or e-readers. Instead, the focus is now focused on Alexa supported smart devices. The shift in focus also meant Amazon no longer attempts to significantly innovate with its Fire tablets and Kindle e-readers. This change in direction is further confirmed in the recent release of an updated Kindle Oasis that is near identical to the previous generation but with an added adjustable warm light. The adjustable warm light feature, to compare, was first announced by Kobo when it released the Kobo Aura ONE in August 2016.