In Sketch we built the color picker directly into the inspector. To see it, select a shape, enable the fill or border and click on the color button in either of them.
A popover window will appear and attach itself to the color box you just clicked. Depending on the kind of color you’re adjusting (A shadow color, fill color or gradient), the inspector will show different options, but most of the time most of the space is taken up by the Color Picker.
The color picker is based on the HSB color model with the Saturation and Brightness on the horizontal and vertical axis of the big square respectively, and then hue on the slider underneath it. Underneath there you can change the opacity of the color.
You can change your color using the text fields below the color picker or by dragging the little indicators around in the color picker. When adjusting the saturation and brightness, notice you can hold shift to restrict moving to one axis.
Below there you can see the HEX value of the color and the RGBA color values. Note you can switch to HSBA color values by clicking on the RGB labels.
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, 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.