In Sketch, the color picker is accessible from the Inspector once you have any layer selected. Simply click on the color button for any fill, border, or shadow to reveal the popover.
The large color picker is based on the HSB (Hue, Saturation, Brightness) color model. If you drag the point horizontally, you can make the color more, or less vibrant, whilst dragging vertically will adjust the brightness of the color.
To change the hue, or tone, click-and-drag the slider below the picker. You can always see a preview of the selected color to the right. You can adjust the alpha, or opacity for the color using the slider below.
You can use the eyedropper button , to the left of the hue and alpha sliders to sample any color on your display. This is a great way to quickly choose a color from your design or an image in or out of Sketch.
With any layer selected, you can change its solid fill color by pressing Control-C to summon the eyedropper tool, and clicking on any color.
Underneath the controls to pick a color, you will see some text fields that contain the color in values that can be translated to code. The HEX value is its own field, along with RGB and A for alpha.
Note: you can switch to HSBA color values by clicking on the RGB label.
By clicking the color preview well (on the right of the hue and opacity sliders), this will reveal a list of your frequently-used colors for the current document, as well as information about how often they’ve been used.
This makes it easy to reuse frequent colors without having to create presets from them manually.