That is not a $1s$ orbital and a $2s$ orbital, the two together make up the $2s$ orbital. If you take a look at the radial distribution function versus atomic distance for a $2s$ orbital, you'll see that there are two peaks and a node between them.
The graphic you presented is (rather poorly) illustrating the above graph of the RDF, with darkness corresponding to the magnitude of the RDF at a given radius. It's useless to try and cut it up so cleanly, though. Electrons don't orbit the nucleus in a well-defined path like the planets orbit the sun—they can be literally anywhere except the node. The only 100% chance of finding an electron in an orbital is by integrating over all space (from center of the nucleus to infinity, in all directions).
The orbital is not where the electron is most likely to be found, it is the region of space that it occupies as described by a mathematical function (its wave equation). In order to understand why we treat quantum mechanics the way we do, I would strongly recommend reading up on the the uncertainty principle as well as wave-particle duality (though work through the math you'll need integral calculus, linear algebra, differential equations, and some probability theory). In essence, we can't really know everything about electrons for sure, but what we can know is the probability that they are a certain way at any given time.