EVF vs back panel Live View
Depends on which camera. AFAIK they'll all give you histograms, although some won't give you one, or won't give you the individual RGB histograms, until reviewing the already taken shot, i.e. not in preview. AFAIK Sony is the only maker yet to give you preview, but do note that how much of the camera settings gets integrated into the preview, and how many extra information displays can be optionally added to it, keeps increasing as the technology develops.
In other words, you simply have to read the specs and reviews for any particular model, and perhaps consult the camera manual (often available online).