Color Picker

In Chrome and Edge, yes — the "Pick from screen" button uses the EyeDropper API to sample any pixel on your display, including from other windows. Firefox and Safari have not shipped that API, so the button is hidden there and you can use the colour field or type a value instead.

They are the quickest way to build a usable palette from one brand colour: tints (mixed toward white) for backgrounds and hover states, shades (mixed toward black) for borders, text and pressed states. The ramp shown gives you a consistent set rather than eyeballing each step.

Because insufficient text contrast is the single most common accessibility failure on the web, and it is invisible to anyone with good eyesight on a good screen. Checking as you pick — rather than after an audit — is much cheaper than retrofitting a whole palette.