Potential manufacturing differences is an interesting topic, and some reports in this forum noted the oposite of your finding (suggesting that K4 simply had a lower grade screen due to the lower price). Now it seems just random
I have the K4 and K3 and I have a hard time deciding if there is a quality difference.
- I think I see greyer letters on the K4 when viewing the screen at a 90 degree angle, but light seems to be better dispersed at an angle. (I might be wrong because the effect isn't that huge). Did you view them at the same angle?
- There's seems to be a slight difference in the shades of grey when rendering images (I assume it's firmware related and might give a difference to KT vs K4).
- The bezel color has an effect on appearence (Which is immediately apparent when comparing the K3 and K4, but the bezel on the KT and K4 is almost the same)