I too, much prefer the easier lighting (not so irritatingly bright | obtrusive in crowds) and battery saving on my SGTab-A: Settings> Display> Vision> Negative Colors ! Actually it affects everything displayed, not just the keyboard, and it is not "negative colors", it is just same colors but "Negative (inverted) intensity". So bright red is dark red, white is black, etc. Since most advertisers, programmers, & web designers want EVERTHING VERY BRIGHT!!!!!!, this contrary setting suits me just fine. Pictures look a little funny, but not irritatingly so, unless I'm doing a lot of photo or video work; in which case, I just turn off the setting for a while. This setting disables a couple of other settings like [Color adjustment]. I hope this helps.
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