What has blue in the subject when sad or un pleased but when you change from blue to green in the end of the same subject what could that mean? Could be a person, place, or thing, or all three.
It is about FEELING.
Both idioms "feeling blue" and "feeling green" are used to express same feeling or situation.
Well, one option is:
Feeling blue means you’re sad or unpleased. Replacing it with green, eg. “Feeling green”, usually means that you’re feeling envious of somebody.