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The Kindles only use so called "White" LEDs, so no "color temperature" change is possible.
I use a nice color temperature of reading light. Or daylight. I don't use the LED front light on my Kobo or Kindle.
It's fake colour temperature on ANY LED front light, LED lighting or LCD using LED back lights as it's a discontinuous spectrum. A fixed "white" is the so called "White" LEDs which are Blue/Violet/Near UV part of spectrum depending on physical type (affects cost). The white appearance is from phosphors.
A CFL, CCFL, Fluorescent lamp is much shorter UV, so the phosphors work better.
Also a better spectrum (better colour Rendition, apparent Colour Temperature is separate) needs shorter UV (no LED) and more phosphors (less light). So high efficiency CFL are very discontinuous and a bit blue, good colour rendition is less efficient. The apparent colour temperature is down to mix of phosphors.
A "White" LED might only have one or two phosphors, cheapest uses just yellow and with blue of cheap LED you get a white appearance. Huge gaps in spectrum.
so called "Adjustable" Color temperature front lights on eInk need either Red, Green and Blue LEDs or Yellow and Blue (cheaper). Both of these are more expensive than blue/violet LEDs with yellow phosphor coating.
LCD panels can do apparent colour temperature change by the LCD itself (which is monochrome but with coloured dye dots on each pixel, either R G B, or R G and G B on alternate lines or sometimes R G B Y). Only very expensive TV / Monitor panels use R G B LEDs instead of "white". Also cheaper LCD panels only use LED at the edges.
The OLED are not "real" LEDs. they are diode like Electroluminescent dots that use phosphors. Only very large hall / stadium displays and the Sony Crystal screen use real R G B LEDs.
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