A simple Color-Picker using CSS5 color-contrast() and color-mix()

Safari is often blamed for being “the new IE of web-browsers”. That's not fair, because Safari has recently been a “first-mover” in a lot of areas. For instance, Safari Technology Preview has implemented a lot of the stuff from the CSS Color Module Level 5 specification – color-contrast() and color-mix() among them.

Let's build a simple Color Picker using these cool new features! We'll add some JavaScript, using CSS.supports, to make it work in other browsers as well.

The markup is a simple fieldset with radio-buttons:

<fieldset class="color-wrapper">
 <!-- start iterate colors -->
  <label class="color" style="--bgc:hsl(168, 41%, 65%)">
    <input type="radio" name="cp" value="hsl(168, 41%, 65%)"><i></i>
  </label>
<!-- end iterate colors -->
</fieldset>

We'll set a custom property, --bgc, for each color, and with a dash of CSS, this it how it renders in Chrome:

Using a mask() for selected color

We'll add a mask with a checkmark-icon to the <i></i>-element:

.color i {
  aspect-ratio: 1;
  background-color: transparent;
  display: block;
  mask: no-repeat center center/var(--ico-w) var(--ico);
  -webkit-mask: no-repeat center center/var(--ico-w) var(--ico);
  width: 100%;
}

In Chrome, it now looks like this:

Better – but the icon will have the same color, even if the background-color is dark, like the example above. It's also a bit annoying, that the border-color is the same for all colors.

color-mix()

With the color-mix-function, we can add a colored border, based on the custom property, --bgc, mixing in 10% of black:

.color {
  border: var(--bdw, 0.125rem) solid color-mix(in hsl, #000 10%, var(--bgc));
}

color-contrast()

With the color-contrast-function, we can change the color of the icon, based on the custom property, --bgc:

.color input:checked + i {
  background-color: color-contrast(var(--bgc) vs white, black);
}

In Safari, it now looks like this:

Cool! See those beautiful, dynamic border-colors! The checkmark-icon is white on dark colors, and black on light colors.

And absolutely no JavaScript is required!

Fixing issues in Chrome & Co.

In non-Safari browsers, we'll have to use some JavaScript in order to achieve the same:

if (CSS.supports('not (color: color-contrast(red vs black, white))')) {
/* code here */
}

We'll add a method that'll iterate the labels of the fieldset, and set a custom property, --ico-c, to either black or white, depending on the brightness of the iterated color:

function setLuminance(elements) {
  elements.forEach(element => {
    const rgb = window.getComputedStyle(element).getPropertyValue('background-color'); 
    if (rgb) {
      const [r,g,b] = rgb.replace(/[^\d,]/g, '').split(',');
      const brightness = (299 * r + 587 * g + 114 * b) / 1000;
      element.style.setProperty('--ico-c', brightness <= 127 ? '#FFF' : '#111')
    }
  })
}

The snippet will return the color of the label as rgb, no matter if it's hex, hsl or rgb to start with, then check it's brightness, and set the --ico-c-property.

In Chrome, it now looks like this:

Much better! The border-colors are still a bit dull in “non-Safari”-browsers ... In the setLuminance-method, we can fix that, by deducting 20 from each chanel (r, g and b):

element.style.setProperty('--bdc', `rgb(${r-20},${g-20},${b-20})`);

Enabling color-contrast and color-mix

In Safari Technology Preview, go to Develop > Experimental Features and enable them:

Demo

Closing thoughts

I tried to use color-mix within color-contrast – but that didn't work!

I guess the implementation is not completely done, and thus a little buggy – but I'm looking forward to being able to mix in 80% white or black with the background-color, so the icon-color blends in more “softly” with the background-color.