For example, for a mostly white (or dark) scene I'm metering (using the evaluative metering mode) does the light meter still try to make the white (or dark) area a middle gray or is this taken into account during the database comparison? In other words will white be white based on the cameras exposure values or do I still have to open up 1 to 2 stops like I would normally do in the other metering modes to make white look white in the final image?

Yes, you are on the right track. As you say, the camera evaluates the scene and compares it to scenes in a database, looking for a scene that matches the lighting and the subject placement (it presumes the location of the active focus point identifies the subject). But like all meters, it's calibrated to presume that the subject is middle gray.


But...it might not actually expose it that way. The scenes in the datbase are examples selected by people and inserted into the database as "correct exposures." Sometimes in a "correct exposure" the subject is deliberately lighter or darker, and if Evaluative can select the correctly matching database scene, it will take this into account.


Sorta.


Evaluative can take into account the effect of the surrounding light patterns and attempts--by the database scene matching--to identify what kind of picture it is. It can determine, for instance, that "this is a backlighted picture" and will thus intentionally underexpose the subject slightly to retain the backlighting ambience...


...but that underexposure will be based on the presumption that the object under the focus point is middle gray. So if the subject is actually a bride in a white dress with the sun as a backlight, Evaluative will make that white dress a bit darker than middle gray.


That's what the compensation control does in Evaluative mode. If the subject (that is, the object you focused on) is not middle gray, use the compensation control to correct for it.