Latex underbrace - change color

[pisoir]

Hello, can anyone give some advice about how to change the color of underbrace? The equation is in normal black color, but I would like to underbrace some of its part, but I want to have the underbrace in light gray. Is it possible to do it?(change the color of the brace only?)
Thank you.

 

[fleem]

$$\definecolor{Blue}{rgb}{0,0,1}<br /> \definecolor{Black}{rgb}{0,0,0}<br /> \color{Blue}{\underbrace{\color{Black}{hello}}}$$

\definecolor{Blue}{rgb}{0,0,1}
\definecolor{Black}{rgb}{0,0,0}
\color{Blue}{\underbrace{\color{Black}{hello}}}