It doesn't need to be - that's perspective. The horizon should be level though, unless it's deliberately a long way out.But now the post isn't vertical
Straightened on my phone.
There aren't any colours in the RAW file at all. I don't mean in the same way that a jpeg is also ones and zeros, but a RAW file doesn't have values for RG&B as a jpeg does, a RAW file has to be converted before being viewed.I shoot in RAW mode which produces almost a digital negative. There are colours in the image as you can see, but not to the extent when you shoot in jpeg mode when your camera will do the "developing" for you.
If you use Lightroom, you won't have to do that, as it will never change your original NEF.When you're happy with what you've done, you can save your file as a JPEG, whilst the original stays as a NEF file as you left it. For example, before I posted the original image below, I had to slide all the sliders back and set everything back, so none of the original file was permanently changed.
And if you've only got one SD card, you can set the camera to record both NEF and jpeg to it.If you've got 2 SD cards, you can set one of jpeg and one for RAW in your camera.