The figure above shows the graphs of four exponential functions, listed below. Match the functions with the colors, using b for blue, r for red, g for green, and y for yellow.

: $f(x) = 2^x.$
: $f(x) = 3^x.$
: $f(x) = \left(\frac{1}{2}\right)^x.$
: $f(x) = \left(\frac{1}{3}\right)^x.$

Hint: Look at $f(1)$.