Merhaba,

As far as I know most of Turkish online courses, which contain the chapter about colors, always teach the simplest question to ask "what color is this" = "bu ne renk?" For example "araban ne renk?" etc...

But recently I attented a Turkish class at a university (first year, complete beginners) and the teacher taught to answer the question about flag colors, for example "Polonyalı bayrak beyaz ve kırmızıdır." Then one of the students asked, how to ask a question "What color is the flag of... ?" and the teacher replied they can´t do that now because so far they hadn´t learned the  tamlama construction. I was a bit surprised what is tamlama needed for in case of colors.. if you can ask simply "Polonyalı bayrak ne renk?" or possibly more correcly "Polonya bayrağın ne renk?" but is it really neccessary to put tamlama into the question about color "Polonya bayrağının ne rengi?"

Polonya bayrağının rengi ne?

What is the color of polish flag?

(Literal translation from turkish: What is the color of Poland´s flag?)

If you insist on using "polish" we can say:

Polonyalıların bayrağının rengi ne? What is the color of polish people´s flag?

only humans can be "polonyalı", not flags or other inanimated things in turkish.

Ok, I understand the thing with Polonyalı bayrak Polonya bayrağı and actually that wasn´t the point of my question. I suppose the teacher told the students to use "Polonyalı.." instead because they haven´t learned tamlama compounds so far. 

But my actual question is-

Why can´t we say Polonya bayrağı ne renk if we say eg. Gözlerin ne renk (what color are your eyes?). Why Polonya bayrağının rengi ne is the only correct option?

Polonya bayrağı ne renk? What color is the polish flag?

Polonya bayrağının rengi ne? What is the color of polish flag?

You can use both of them. Meaning is almost same.

Emphasis is a little bit different. Polonya bayrağı ne renk? In this sentence you are more interested in the color type. Polonya bayrağının rengi ne? In this sentence you are more interested in the polish flag, not french flag or german flag.