Imperial Halo
Imperial Halo (#664ADB) is a true indigo with a vibrant character. It holds its own as a focal accent, carrying visual weight without tipping into neon territory. Its HSL profile (252°, 67%, 57%) places it in the balanced band at a mid lightness. It works across type, buttons, and borders, saturated enough to feel deliberate but balanced enough to not fight the rest of the palette. For a confident two-color system, pair it with its complementary yellow. For something softer, pull in its analogous neighbors on either side of the wheel.
Etymology
From the Latin imperialis, of the empire — applied to color since the medieval period for the hues reserved for sovereigns and empires: imperial purple of Tyrian dye, imperial yellow of Ming-dynasty porcelain. As a modifier, imperial implies saturation combined with the institutional weight of a color owned by a court. Sits in the bold-and-deep corner, alongside royal.
Greek hálōs, threshing floor — adopted into Christian iconography as the circular disc behind the head of saintly figures, traditionally rendered in ultramarine lapis-and-gold-leaf in Greek-school and Russian-school icon panels. Halo color refers to a 14th-century Russian-school Theotokos icon's halo field: a saturated, slightly cool deep blue-violet with the matte finish of egg-tempera-bound ultramarine over gesso ground.
Closest matches
The nearest named color in three reference sources, ranked by perceptual distance (ΔE76 in CIELAB). ΔE < 1 is imperceptible to most viewers; ΔE > 10 is clearly different. When two sources point to the same hex they’re merged into one tile; click any to open that color’s page.
Variations
Click any swatch to exploreHarmonies
Accessibility
How this color appears to viewers with the four major color-vision-deficiency types. Computed via the Machado (2009) physiologically-based model. If a tile matches the original, the color reads the same to that viewer.
The color used as foreground text against pure white and pure black, with the contrast ratio and WCAG 2.1 grade. Aim for AA (4.5:1) for body text and AA Large (3:1) for 18 pt+ headlines; AAA (7:1) is the gold standard for long-form reading surfaces.
Wide gamut
The CSS Color 4 wide-gamut form of this color. Both swatches render the same color on every display — the P3 form only diverges from sRGB when a designer pushes channels outside sRGB's reach.
This color is chromatic enough that authoring it as P3 native (instead of clamping to sRGB) gives a perceptibly more saturated render on wide-gamut displays — modern Macs, iPhones, iPads, and most recent OLED laptops.