Because blou comes after the verb is, it is being used as a predicative adjective.
In Afrikaans, adjectives used after a linking verb like is normally stay in their basic form. So:
That is why you do not add anything extra to blou here.
Yes. Afrikaans uses is with all persons in the present tense of wees (to be).
For example:
So unlike English, Afrikaans does not switch between am, is, and are.
Blou is pronounced roughly like English blow, though the exact Afrikaans vowel quality is a little different.
So the whole sentence is approximately:
dee lint is blow
That is only an approximation, but it is close enough for a beginner.