From a handout I prepared for my students last year
Bán: white, fair, fair-haired, pale.
Bán is the colour of white cloth, frost, white wine, silver, white or fair hair, and pale, pallid, or blanched skin. People with albinism are described as bán.
Bán is used in terms of endearment: mo chailín bán, “my fair girl” regardless of hair colour. Idiomatically, bán is used to mean ‘empty’ or ‘blank’: a leathanach bán is a blank page, while an áit ban is an empty or deserted place.
Geal: white, bright, clear.
Geal is the colour of white flour, lime, the sun, teeth, snow, and swans. It describes bright light, and clear days. Like bán, it is used in terms of endearment: a ghrá gheal, O fair love.
Fionn: white, fair.
Fionn is the colour of sunlight, seafoam, and fair hair.
Bán, geal, and fionn all overlap significantly. Bán generally is the most common, and tends not to refer to shades which can be described as bright or shiny – however silver money is described as airgead bán. Fair hair is never described as geal, although fair skin is.
Liath: grey, pale grey.
Liath is the grey of grey hair, animals like mice, mist, mouldy bread, and watery milk. Unlike geal, it is a dull colour. Idiomatically, liath can mean “ancient.”
Buí: yellow.
Buí is the colour of sunlight, gold, cornmeal, tanned leather, dried fish, and tanned or sallow skin. Idiomatically, buí is used to meán “ugly”, an gadaí buí meaning “the ugly thief.” A fear buí is an Orangeman. Seán Buí is John Bull, or by extension, England as a whole.
Dearg: dark or vibrant red.
Dearg is the colour of red ink, blood, gore, fire, embers, hot iron, and the lower layers of soil. Fíon dearg is red wine. Idiomatically, it can mean “real” or “intense”.
Rua: brownish-red, copper, russet.
Rua is the colour of red hair, chestnut horses, copper, and rust. Idiomatically, it can mean “strong” or “violent”: an oíche rua is a stormy night. A madra rua is a fox. In place-names, such as An Cheathrú Rua, it refers to high iron content in the soil.
Corcra: purple. An early loan-word from Latin purpura, before Irish had a p sound.
Gorm: blue, but also bluish green, deep green, and deep purple.
Gorm is the colour of indigo, azure, discoloured potatoes, the deep-blue colour of the sky, lush vegetation and grass, blue or green eyes, and bruised or livid skin. A duine gorm is a Black person.
Glas: green, but also grey and light-blue.
Glas is the colour of the sea, grass, young or unripe plants, and green timber. It is also the colour of undyed wool, homespun cloth, iron, a cold winter sky, and grey eyes. Idiomatically, it can mean new, unexperienced, fresh; a saighdiúir glas, green soldier, is a new recruit.
Uaine: bright green.
Uaine is typically used for any artificial green: one of the colours of the Irish flag, green paint.
Donn: brown.
Donn is the colour of brown hair, cattle, brown paper, and timber or wood. Idiomatically, it can mean “firm”, or “strong.”
Dubh: black, dark.
Dubh is the colour of black hair, night, ravens, and coal. Idiomatically, it can mean gloomy, evil, in secret. A place which is dubh le daoine, black with people, is overwhelmingly crowded. To have a croí dubh, black heart, is to feel overwhelmed by sorrow. An Fear Dubh is the devil.