Is My Invention Patentable?

Any novel, useful, and non-obvious invention can get a US Patent

Per US patent law, any person who "invents or discovers any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof, may obtain a patent.  When most people use the term invention, they are typically referring to a physical device or machine, but practically any new idea can be classified as a new or improved “useful process, machine, manufacture, or composition of matter".  Clear exceptions are laws of nature, physical phenomena, and abstract ideas.

Basically, if you create it you can patent it; if you discover it you can't.

Beyond these criteria, there are some key rules to remember - the USPTO grants patents only to inventions that are:

Novel
The word "novel" is often used to mean "clever", but here it simply means "new".  Your invention is no doubt clever, but to get a patent what really matters is that it is new.  For the USPTO, that simply means that the invention must not have been already invented by anyone else.  Note that the last sentence said not invented by anyone else.  That it hasn't already been patented is not sufficient. If anyone anywhere in the world (not just in the country in which you are seeking a patent) has previously reduced the invention to practice, published a description of the invention, etc., only that person can patent it, and only within a year of public disclosure (e.g. an offer to sell the invention or any publication made available to the public).

Useful
Your invention must be useful.  These days, the USPTO does not take exception to virtually any invention based on an assessment of its utility, other than insisting that it actually must perform the stated function.  Naturally, the burden of proof varies according to the credibility (or incredibility) of the invention's stated capabilities.

Non-obvious
When we discussed novelty above, we said that the real crux of the matter is for the invention to be new, but it must be clever enough to be not absolutely obvious.  Things like color changes and equivalent material substitutions (substitutions that don't fundamentally improve an invention) won't be considered non-obvious.  Generally, if your invention is novel, chances are you've met the modern interpretation of the non-obviousness requirement.