"It is not the same color."
Translation:Det är inte samma färg.
a) färg is an 'en' word so 'färget' is not a word, the definite form is färgen
b) samma is a special adjective. It's always used like this: no front article, and the noun is indefinite.
A normal adjective works like this: you can say en röd bok or den röda boken 'a red book' or 'the red book'
With samma, you only have one option: samma bok 'the same book'. In English, 'same' is also an exception in that you don't really say 'a same book', only 'the same book'.
This is because samma has a meaning that makes the expression definite in itself.