Объясните происхождение цвета: а) синего неба; б) синего стекла; в) синего листа бумаги

I'am not a veri sosiable person yet there are people whom i can call friends. One of them is Ihor. Her is eighteen.  Ihor is a future economist.  He is a first year student. We often go to the cinema, cafes, concerts and shows. Ihor is good friends.  He's always readly to help everibody who needs.  I'm happy to have such a good friend  as ihor.