じゃないis the way to say something indirectly.

So if you say わたしは　りんごが　すきじゃない, it means I don't like an apple

And わたしは　りんごが　きらいじゃない means I don't dislike an apple. (but I don't want to eat it)

So in my opinion, if i hear someone says きらいじゃない, i assume something negative will follow after that like what i wrote in the bracket above.

Does this help you?
I'm more than happy to explain more so please ask me if you have further questions.
It will be a good English practice for me!

I think that we tend to express something directly. Instead, we prefer to describe vaguely. 

すきじゃない: I honestly dislike it, but I don't want to make you feel bad. Therefore, I say すきじゃない

きらいじゃない: I like someone or something, but I feel embarrassed or I don't feel like to say it. So, I usually say わたしは　かれが　きらいじゃないor あかいろが　きらいじゃない。

I wish I could help you.