In childish representations of outdoor scenes, the sky is blue and the grass is typically green. A child will colour the grass one shade of green, and the trees maybe another, (light and dark are the usual options). The detail is not so important to a child. Green is green. On the other hand, to a mature artist trying to authentically portray the scene they are painting, green is not just green.
There are, in fact, many shades of green: light and dark, lime, emerald, olive, khaki, asparagus, and myrtle and many more besides.
Next time you walk along your street, look closely at the greenery and you will be amazed at all the different hues. Even the grass is not just green. There are numerous shades.
A man was having a conversation with a Christian who brought up the subject of the Bible. The man replied, a little contemptuously, that the bible was just a history book with no relevance today. Merely a diary. Many others have dismissed Jesus Christ as simply a good man, a moral leader or even a great religious teacher, but just a man, nothing more. Surely, these people are the very same ones who only see green when they look at the trees and the grass. They don't care to delve into what lies beneath the superficial. They probably don't want to believe the reality of different shades of green because it makes things too complicated. Nor do they want to accept the reality of the Bible being a God breathed, powerful and relevant collection of books because that would upset the apple cart of their world view.
To accept these truths requires the humility to admit you have at best been ignorant about the shades of green, or at worst deliberately ignored them and denied their existence.
Look out of your window now, and tell me what you see.