Google's color system is called HCT:
- Hue is what we commonly think of as "color", it takes values in
[0, 360] - Chroma is how vibrant the color is, it takes values in
[0, 150] - Tone is the shade of the color, it takes values in
[0, 100]
In the grid below, the horizontal axis represents variations of tone, while the vertical axis represents variations of hue. A tone of 0 is always black, and a tone of 100 is always white. When the chroma goes to zero it transforms all tones into shades of grey.
What's interesting with this color system is that it tries to be as perceptually accurate as possible: for a given hue and chroma, all tones seem to belong to the same family of colors. This makes it very easy to create a color palette starting with a seed color.
Another feature of HCT is that it is accessible (in this case, compatible with people with visual impairements): it guarantees that 2 colors picked 40-50 tones apart will always have high enough contrast, e.g. such that one could be a background color, and the other a text color on top of it.
3D
We can visualize those three components on a color wheel.