P3 is a wider color gamut than sRGB: it has up to 35% more colors, but not all screens are able to display them. Below are some examples of P3 exclusive colors (expressed with the oklch() syntax) along with theire traditionnal RGB/Hex fallback.
On a non-P3 device, both left and right will display the same color. On a P3 capable device (like Apple iPhone™, for instance), the colors on the left hand side of each row should be much more vivid. Those are a few of the colors covered by P3, but not sRGB.