Pick a colour visually and get every format, a tint/shade ramp and live WCAG contrast feedback.
#2563ebrgb(37 99 235)hsl(221.2 83.2% 53.3%)hsv(221.2 84.3% 92.2%)cmyk(84.3% 57.9% 0% 7.8%)oklch(54.61% 0.2152 262.9)Click any swatch to copy its hex value. Tints (lighter) work well for backgrounds and hover states; shades (darker) for borders and text.
Pick a colour visually and read its value in every format at once, which is quicker than converting between notations by hand when you are still deciding what the colour should be.
Judge a colour in the context it will be used rather than against the picker's background. A swatch that looks right in isolation frequently fails once it is text on a page, which is why checking the contrast ratio of the pair is a separate and necessary step.