Three fourths of the earth consists of water, and one fourth is land which in ancient times was covered by dense forests. Thus the colour of water, blue and the colour of vegetation on earth, green, are the most visible colours.
Science has its own reasons for the water appearing blue and vegetation appearing green but we are discussing these issues in relation to God; hence our answers would be sentimental and philosophical.
Wherever there is the union of purity and depth it produces blue colour. The water of the seas and the sky both are blue. Hence the colour blue is also called sky colour. Lord Vishnu, Lord Krishna, Lord Ram are all blue coloured. Meghavarnam Shubhāngam or Kekī Kanthābhnīlam. Since God combines both purity and depth or boundlessness hence God too is blue.
The colour of earth or sand is yellow. The gold, which is mined from the earth, is also yellow. In our scriptures Radhaji is also described as yellow or fair coloured. Kanchanvarnī Radhika Sajal jalad Ghanshyām.
According to the science of colours, there are three primary colours: Blue, Yellow and Red. Various permutations combinations of these three basic colours obtain all other colours which means green is made by mixing colours. How? Green is obtained by mixing blue and yellow. In this sense, green symbolizes the union of Radha and Krishna.
The colour of earth is yellow and when it mixes with the blue water, or when it rains on the yellow earth the union of both produces green vegetation. Green colour is also believed to symbolize peace and tranquillity. God by nature is absolutely peaceful and tranquil. The human soul too by its nature is the same, but by virtue of his misdeeds man sometimes becomes red with rage and burns others or burns himself with jealousy.
Since man also is a part of God, he should remain pure and rise above his narrow limitations. He should become vast and boundless and expand his consciousness. He should lovingly accept all humans and creatures as beings of the same spiritual self as himself and be one with them so that blue and green or tranquillity gets imbibed in his life.
Thus, from this viewpoint we can see and understand why God chose blue and green more than the other colours.
