The saturate() CSS function is used to adjust the intensity of colors in an element by increasing or decreasing their saturation. Saturation refers to the vividness or purity of a color - higher saturation results in more vibrant colors, while lower saturation moves colors toward gray. This function is commonly applied through the filter property, allowing designers to create visual effects like highlighting elements, desaturating images, or enhancing color contrast without changing the original image.

The value provided to saturate() is typically a number, where 1 represents the original color, values greater than 1 increase saturation, and values between 0 and 1 decrease it. Setting the value to 0 will make the element completely grayscale. For instance, saturate(2) doubles the color intensity, whereas saturate(0.5) reduces it by half.

A practical example is enhancing an image on hover:

img:hover {
  filter: saturate(1.5);
  transition: filter 0.3s ease;
}

Here, the image becomes more vivid when a user hovers over it, creating a subtle interactive effect. The saturate() function can be combined with other CSS functions like CSS brightness() or contrast() within a single filter declaration for more complex visual enhancements.

This function works on most elements that support filter, including img, backgrounds, and SVG graphics.