The blue and yellow lines are exponential moving averages (EMA).  The EMAs are a weighted average of the closing price, over a defined number of periods, with more weight given to the most recent price.  I don't know exactly how the lines are parameterized, but it's probably described in more detail in the corresponding forum thread:  https://bitcointalk.org/index.php?topic=43514.0.  You can disable the lines with the link directly underneath the chart: "Hide EMAs".