After I've exported my last couple of videos, I've noticed something strange going on with the colors. At certain points they kind of look warbly. This is not Youtube processing as the original file looks this way as well. It shows in the example below in the first few seconds of the video. It happens mostly on grass. I do adjust the colors on all my clips (though I'm just learning, so I'm not great at it), so I'm wondering if its something I'm doing. It does NOT look like that before I export though. Thanks in advance for any help!
I agree with Sumeet, it looks like compression artifacts. Exporting to a high quality codec (like Prores HQ) should solve the issue. Or if you want to use H.264 (which you are probably already using) - increase your datarate.
You might currently be using the H.264 'match source - high bitrate (or medium bitrate)' presets when exporting from Premiere Pro? If not try the 'match source - high bitrate' preset under H.264.
If you were already using this preset - try increasing the datarate in this preset. You'll find it in the 'video' tab in the export window, scroll down to 'Bitrate Settings' and change 'Target Bitrate' from 10 to 20.
See how you go.
Keep in mind high detail elements (like grass) are always going to be the hardest images to compress and keep looking OK - AND once uploaded to YouTube will always suffer the most once re-compressed by YouTube.