Why such oddities with a white background in H.264?

Question

Video processing

Greetings!
We have a video without compression with a white background. We press in H.264 (how exactly - I don’t know, a video specialist is engaged). We get a gray background.
Google, read and see that the range in H.264 is 16-235, instead of 0 - 255. The question is - is it always like this or does it depend on the settings or the type of compressor?
Then the weirdness begins. When we embed a video in an HTML page with the video tag and watch it, for example, in Firefox 30 (Win7), the gray color is different than when viewed, for example, in the system video player. Well, this is explained by different decompressors. But! When scaling a video in Firefox (not zoom in the browser, but the attributes of the video tag), we get a arbitrarily and unpredictably changing background color from one load to another. How can this be explained?
I assumed that the background is not solid, but grainy, and when scaling at the compressor level, this leads to the fact that the main background color is randomly formed. And if you zoom with a browser, then the zoom comes after decoding and scaling no longer affects. Or nonsense?
Alas, I can not provide a sample video yet - copyrights! Maybe a little later - a fragment.

Answer 1

I also steamed for a long time with different colors in the browser and the system player, the same VLC has not yet figured out that they are played through different video "engines" in the system. In the browser, the colors depend on the settings of the video card, and the decoder, that is, the player, while for system players everything works somehow more cunningly and something else in the layer.
Twirl the colors of the video card settings, this will work for the browser but not for the system player.
I admit that H.264: 16-235 may well cut. The compressor settings are different for everyone depending on the vendor, so please refer directly to the documentation of your encoder, which I'm afraid you will not find, which was a surprise for me.)
vimeo.com/help/faq/watching-videos/playback-issues.. .