They sure do. Colours are adjectives. Aside from a handful of invariable adjectives, you always need to change the ending of the adjective so that it agrees with the gender, number and case of the thing it's describing.
μπλούζα is a feminine noun. There's only one of it, and it's the subject of the sentence, so it's nominative singular.
In the singular nominative, green is: πράσινος in masculine, πράσινη in feminine and πράσινο in neuter.
So, we have μία πράσινη μπλούζα. If we were describing a green car - αυτοκίνητο - that's a neuter noun, so we'd have ένα πράσινο αυτοκίνητο. A green sky, sky being masculine: ένας πράσινος ουρανός.
In Wiktionary, most common words have declension tables, and you'll find yourself referring to them a lot!
Hope that helps a little.