Periwinkle (#CCCCFF) is a very light, highly saturated blue hue. Periwinkle is a pale blue-violet named after the flower; Pantone's Very Peri was 2022's colour of the year.
In RGB it is made of 204 red, 204 green and 255 blue. Its HSL hue angle is 240° with 100% saturation and 90% lightness, while its perceptual OKLCH lightness is 86% with a chroma of 0.070. For print, a starting CMYK mix is 20% cyan, 20% magenta, 0% yellow and 0% black.
As a text color on white, Periwinkle has a contrast ratio of 1.54:1, which fails WCAG AA even for large text. On black it reaches 13.65:1 and passes AA for normal text. If you use Periwinkle as a background, put black (or very dark) text on it. The APCA lightness contrast is Lc 79 for black text and Lc -28 for white text.
Its perceptual complement is #D8D59F, close to apricot. Colors that look most similar are mauve, powder blue, lavender. It looks fairly similar to people with red-green color blindness (ΔE 2), so its meaning mostly survives.