Not wanting to beat a dead horse, but modern DC wiring is referred to as "positive and negative" to avoid any confusion with AC wiring. As far as accepted color codes, the US and EU have very different colors for the positive and negative DC leads, and I'll just stick with US color coding for this discussion. And yes, the negative is also the ground in modern DC electrical systems.
Red is generally referred to as the positive lead in DC, with black as the negative lead. This goes awry rather quickly when red is not present in a 12VDC circuit. Without the presence of red, BLACK is generally considered the positive with WHITE as the negative. Other colors (other than white) can also be used for a negative lead when paired with black (but NOT RED!)
Confused yet, don't worry...........If you have a boat, the accepted color coding is red = positive and yellow=negative. it degrades rapidly from there!!!
When working on DC circuits, it's always a good idea to keep a volt meter handy so you can physically check the polarity of your wiring
. This is especially true if some unwashed tech has touched the wiring and had no idea what they were doing (I've seen it more times than I care to enumerate!).