When you use an adjective to describe a noun, the adjective usually comes after the noun.
Remember:
Madainn mhath! Good morning!
Feasgar math! Good afternoon!
If the noun is feminine, the sound and spelling of the adjective can change.
Mar eisimpleir:
Masculine nouns:
Calum beag
little Calum
geansaidh mòr
a big jumper
Feminine nouns:
Anna bheag
little Anna
lèine mhòr
a big shirt
Colours are adjectives too and therefore, the same rules apply. Mar eisimpleir:
geansaidh dearg
a red jumper
lèine dhearg
a red shirt
Therefore, we can tell that the word lèine is feminine and that geansaidh is masculine.