Adobe Photoshop has had a color picker that hasn’t changed significantly for many versions. There is a hue slider, and a brightness/saturation gradient square in which you can pick the color you desire by clicking directly on it.
If you’re like most people, you often want to pick pure black or white, or a pure saturated hue such as 100% red form the picker. Yet you try and try to click close to the corner, and you always seem to get a value that is just slightly removed – it is really hard to get the picker directly on the corner as you click.
Not to worry! Just place the cursor in the middle of the picker field, and click and drag towards the corner, and right off the edge of the chart (for white, in the example above, drag in the direction of the arrow). The picker will be left stranded in the corner, with the exact value you want! Easy, but not obvious!