1. We have no 'KI NI RO' this word, so KINIRO must describe "KI N I RO" 2. If it is written by hiragana we can easily recognize,because as you know our characters describe only one sound. Ki N I Ro, き ん い ろ。

Well... as japanese is written in hiragana (and not in romaji) you'll always know. If you don't know how to write the word, pay attention to the pronunciation: in 金色 (kiniro), the n sound is held for a considerable time, almost causing a small "pause" in your speech, while in "あなた" (anata) there isn't this kind of thing.

金 is kin and 色 is iro. They are separate ideas, so you can't use the "n" from kin and "i" from iro. The way to distinguish them in speech is as said to listen to the pronunciation. "ki n i ro" is a one character longer than "ki ni ro" (which isn't even a real word). There's a small pause after the n. (Because you need to pronounce every character the same amount of time in Japanese) This can also be heard in words like こんにちは konnichiwa and 女 onna and all other words with double n's.