英文句子錯與對?

你要表達的意思是「我們並非專門於某一種生產技術」。

最好將specialized改成specializing，將for改成in，就沒有問題了，specialize之後用in，意思是專門於某一種知識/行業/工作等。

根據這裏你要表達的意思，are之後用specializing或specialized是一個以動詞形式來作形容詞的作用，這個specializing和specialized在英文文法上稱為present participle及past participle，並非過去式或是現在式。在英文文法裏，利用動詞作為形容詞是很常見的。如要表達某人專門於某一項技術/專業等，就要用specializing(present participle)；如要表達某一件物件/機器/物料等等死物專門於某一項技術/專業等，就要用specialized(past participle)。

例如：
Mr. Chan is specializing in marketing.
This machine is specialized in knitting.

wongsir的解答是正確 !

Sorry , we are not specialized for this yarn quality with rainbow color.
應是:
Sorry, we are not specialized for the quality of this yarn with rainbow color.
改了為: the quality of this yarn. (this yarn quality is not right english, such as: this man's name is Jacky 應寫為: the name of this man is Jacky.
are 後面係用過去式, 無錯.

It's not correct. the sentence should be:
Sorry, we have not specialized for this yarn quality with rainbow color.
or
Sorry, this yarn quality with rainbow color is not specialized by us.

對Correct
are 後面係用過去式(passive voice)