kura kattaと言い、kattaの意味は？と聞かれ。

Katta is sort of like saying "was" instead of "is".
you can use it past tense and negative by useing "kura katta".

と説明すればいいでしょうか？
もっと他に良い言い方があれば教えてください＾＾

I think kurakatta is one word. It is past tense of kurai. Katta doesn’t mean anything. If katta meant "was" like you said, you would be able to use katta for any adjective, which is incorrect.