It's true - and important to understand so we can put this "tweaking" nonsense to rest...
The image a camera produces (regardless of the camera!) has two "images" when you press the shutter: what is captured and what is presented. Most cameras don't let you see the "what is captured" image (aka "RAW image") though there are many that can.
Here's a good example:
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RAW Barn - as recorded by my Nikon D700, 14-bit RAW
The sensor does its best to capture the most dynamic range across all channels (RGB and sometimes a dedicated fourth channel). It then takes that photo and processes it through various algorithms, compares it against database images, and then converts that to what the user sees on the screen.
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JPG Barn - as converted in camera by my Nikon D700, "Normal JPG"
The image above has not been edited, adjusted, or otherwise "tweaked" by me. This was done based on Nikon's programming and output under the "Neutral" JPG setting. The color space has been compressed but many colors have been saturated. Contrast has also been increased, while adding some sharpening to hard edges. The camera is giving me what it thinks I want and what is generally pleasing to the masses by closely matching what the eye "sees". The outputs can be manipulated greatly depending on settings picked (user selected or default).
Of course, what the camera thinks the eye sees is rarely what is actually seen. Our eyes are amazing - with different "channels" for color, luminosity, sharpness, etc. Cameras do their best but "tweaking" an image is usually the only real way to bring out the images "true colors"...
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RAW file, cleaned up (wire removed), levels adjusted, colors adjusted and sharpness added to better reflect reality.