I thank you for the reply, but that doesn’t actually alleviate the problem or inform me why it’s being so damn dumb.
I tried rendering short clips (10 seconds) of video in every presetting there is until I found a combination that was /okay/. But it makes tweaking contrast, brightness, gamma, saturation, and white balance a game of trial and error for (in today’s case) 4 solid hours.
One thing of note which may help describe my issue, when taking it from my camera and not touching it AT ALL, it is blown out and bright white. Rendering doesn’t change that fact, despite Sony Vegas PREVIEWING it perfectly fine.
Take a look at this thumbnail image of a RAW video file (.mov) that i’ve not touched.

Here is the same file opened in VLC media player (all other players do the exact same thing), again – untouched.

Here is the same file, again untouched, simply opened in Sony Vegas.

I don’t know what aspect of the file is being /completely screwed/ in video players, but rendering perfectly fine in Sony Vegas.

Thank you so much for your help, though. I do appreciate it!