With Hive Keychain you can choose how "hot" it is. If you only store your posting key there, it can only sign posting-level transactions, which are generally the transactions that require the lowest level of security. eg. Votes, posts and comments
You can store your active key (which is used to sign transfers and other monetary transactions) in Hive Keychain or store it in a paper wallet or where-ever else you choose. If you keep it offline then it is equivalent to "cold storage".
There is a higher level key known as the "Owner Key". That is used for changing your keys and other transactions that require the highest level of security. Hive keychain won't even allow you to store it in the app.