You may define your own custom colors. Here is a dark blue defined in terms of the RGB (red, green, blue) color model.
\usepackage{color}
\definecolor{MyDarkBlue}{rgb}{0,0.08,0.45}
\color{MyDarkBlue}This color is MyDarkBlue
©
\usepackage{color}
\definecolor{MyDarkBlue}{rgb}{0,0.08,0.45}
\color{MyDarkBlue}This color is MyDarkBlue
©