That's a rounding loss, not a change to "your color space". In any case, JPEG supports storing RGB instead of YUV 4:2:0 (or even YUV 4:4:4).

WebP _doesn't_ support this, but it really doesn't matter. The point of image files is for you to look at the image, not at the pixel values.

From the article I cited:

"In fact, of the 16 million colors in the 24-bit true-color pallet, JPEG can only store about 2.3 million colors. That's about 14% of the available color space."

and

"If JPEG stored images using RGB, then the Q tables would cause colors to diverge. For example, blue would have the most loss due to compression so images would appear more reddish and greenish. Instead, images are converted to a different color representation: luminance, chrominance red, and chrominance blue (YCrCb). Changing any one of these values alters the red, green, and blue components concurrently and prevents color divergence."

The article you cited is nonsense. Quantization which causes one of the color channels to get darker is called a "DC shift" and encoders try very hard not to introduce it.