In the RGB additive color wheel (light) the opposite of green is Purple.
In the RBY subtractive color wheel (paint)the opposite of green is Red.
In the CMYK print color space (on paper) the opposite of green is a magenty-purple.
Then it all depends on what kind of green, it's saturation and brightness.
Color science is a thing in several industries.
I define love (and many will disagree) as self sacrifice for the benefit of another. I define hate as self sacrifice to the detriment of another (again, others will disagree). As others will point out, these are very limited and might not capture the love of a child for a parent, and I'm ok with that. I think we use these terms too loosely in general: "I love my phone" or "I hate my new haircut." I prefer to use "like" or "dislike" in these contexts. I would not self-scrifice to harm my new haircut. However, if I love my home, I will sacrifice my time and effort to make it better.
For example, I love my children so I want to be engaged in their lives, I forgive them easily when they make mistakes, I do not think twice about helping them if they vomit or can't make it to the toilet in time, and I am excited and optimistic for their future. For other people, I might not naturally have the same kinds of reactions.
If you buy this definition of love then the opposite would be cynicism, which would produce both apathy and hate depending on the situation.