The histogram on many digital cameras almost always uses the current JPEG settings for displaying a Live View image. Nikon is the worst offender here; Canon generally has done a better job, generating a Live View image with some enhancements for easier focusing.
Cameras vary in how the implement Live View, so check your own brand and model for specifics in reference to the JPEG settings and other features (such as focus peaking).
Nikon D800E example
Nikon’s Live View mode incorporates all the JPEG settings(“Picture Mode”) into the Live View display, even if shooting in RAW-only.
Since focusing in Live View mode is almost always done for focusing accuracy, Nikon’s approach is counterproductive. Live View focusing ought to help the photographer focus as accurately as possible (focus peaking, etc).
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