嘘をつけ。本物のブロンドはもっとナチュラルだし、そんな不自然な金色にはならん。
that's a lie, real blonde (hair) is more natural, THAT kind of of golden (hair colour) totally cannot be (real)?
...にはならん = not 本物/ナチュラル at all? The golden hair colour is what it is, so it would be hard to negate that directly.
On a side note, is there any difference between the literal にならない - aka the negative of になる、 and the negation usage of にならない (話にならない, 洒落にならな.. 問題にならない , etc)
I guess random sentence could be used for the literal meaning.
「パパみたいにならないでね」という母親のグチが子どもをダメにする
Is there any perceived difference? Don't become like your dad vs You're not like your dad at all(doubt this is the case)