Blue colors: from sky to navy
The largest slice of the cool half
Blue spans roughly 230° to 285° on the OKLCH hue wheel, one of the wider bands, bordered by cyan on the green side and purple on the violet side. Pure sRGB Blue sits near 264° and the popular azure Azure near 256°. The edges are approximations, and the data contains blue-violet colors close to 285° that could just as reasonably be called purple.
No lightness rule applies, so every depth from pale to near-black is included. See the other families from the colors hub.
Dark and saturated, rarely light and saturated
Blue is unusual in sRGB because its maximum chroma, around 0.31, happens at a low lightness near 0.45, the lightness of Blue itself. High-chroma blues are therefore dark; lighter blues must give up saturation. Cerulean has a lightness of 0.71 but chroma of 0.13, and Sky Blue is down near 0.07.
Tints of blue therefore drift toward pale grey-blue, and shades toward Navy, which has a lightness near 0.21. The pure primary can look electric and even shimmer next to red, which is why many interfaces use a calmer Royal Blue or Sapphire for primary actions. The picker lets you compare a few before choosing.
Blue as the default interface color
Blue is the most common choice for links, primary buttons and corporate branding, and users have learned to read blue underlined text as clickable. That familiarity is a strong reason to keep the link blue distinct from any decorative blues in the layout.
Contrast is easy at the dark end: Sapphire reaches about 7.2:1 against white and Cobalt about 13:1, both safe for text. Royal Blue manages roughly 4.8:1 and passes AA, whereas Azure falls to about 3.8:1 and suits large text and controls only. Blue is the hue best preserved under red-green color blindness, so it is often paired with orange for accessible two-color schemes; blue and purple can still blur together for some viewers. Check ratios in the contrast checker and the contrast pair pages.
In practice, blue scales are easiest to build by holding the hue near 255° to 265° and stepping lightness in even increments from about 0.95 down to 0.25, trimming chroma wherever the sRGB gamut would clip. Expect the middle steps to carry the most color and the ends to look almost neutral. Hue drift is the usual flaw: blues made in HSL tend to slide toward purple as they darken, so keep an eye on the angle. Pale blues make convincing backgrounds, while the darker ones work for text and headers.
Blue shades to know
A short list: Navy, Royal Blue, Sapphire, Azure and Cobalt. Blue is commonly linked with trust and calm in business contexts, with the caveat that it is a cultural tendency and not a guarantee; the blue color meaning guide goes into detail. Evaluate software for building blue palettes in the comparison hub.