Actually it is either. The positive means that you don’t care much but you care less about other things. The negative says that you cannot care at all about it.
A might bit careless there. Which phrase to use depends on what you mean. The problem is that people use them interchangeably, when they are two totally different concepts.
Here's a real grammar brain twister. ROUTE . Pronounced two different ways for no particular reason, but always spelled the same.