赤 is generally understood as meaning 'red' (which can explain combinations like 赤子 (red face of a crying baby)). However, I have seen some words with 赤 that have a negative meaning, 赤 possibly ...
This question about colours got me thinking: Why, and how, did オレンジ come to replace 橙【だいだい】 to refer to the colour orange? It seems weird to me that a 外来語【がいらいご】(word taken from a foreign language) ...
青 ao seems to be used very much interchangeably for both blue and green. Why is that so, and how does 緑 midori play into this?