Interesting comment from Thom Hogan's D750 User guide:
D750 Guide 100
Before leaving the matrix metering, we need to discuss one other thing: brightness. One relatively common complaint that began with the launch of the D3 and D300 was that the new Nikon cameras “overexpose.” But if you look at some of the images these people are objecting to, they are not actually overexposed (i.e. the highlights aren’t blown out).
Nikon’s interpretation of mid-range brightness changed with the D3 in 2007. The Standard Picture Control has a default Brightness setting of 0. But this produces mid-range tonalities that are somewhat higher in value than the D2 series and other earlier Nikon DSLRs produced. Where a D2x might have placed a value at 122,122,122 the D750 models place that same value at something more like 128,128,128, which appears visually brighter. Meanwhile, highlight and shadow values didn’t change. Thus, to some this looked like “more exposure.” It isn’t. It’s just an adjustment curve. If you shoot NEF (raw) you’ll be able to override that. If you shoot JPEG, you’ll have to learn about the Picture Control settings to adjust this.
The reason for discussing this with the metering system is that you need to be careful to assess exposure separately from tonal placement when you’re trying to figure out the metering system. Picture Control settings are a little tricky, and interact with exposure settings in how mid-tones are visualized.
The matrix metering system in the D750 has a tendency to produce images that don’t strongly blow out any highlights, though this can sometimes make the image look a bit dull and underexposed. The simplest way to deal with such images is to change the linearity using a Curve in Photoshop. Another way is to alter the camera’s settings; in particular, you can use a Custom Curve or change in Brightness in your Picture Control Yet another method is to use Active D-Lighting.
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I'm a JPEG shooter, so I typically use Active D-Lighting on Auto when using Matrix metering. When using center-weighted or spot I turn off Active D-Lighting. I'm of a mind to use exposure compensation rather than adjust the metering system using the b6 setting. --OCD