Filling a path with a color and a pattern simultaneously

pattern is also a kind of filling. So it overwrites the fill option. But you can use preaction to fill the path with the color before it is filled by the pattern.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{patterns}
\begin{document}
\begin{tikzpicture}
\path
  [pattern=bricks]
  [preaction={fill=gray}]
  (0,0) rectangle (5,-1);
\end{tikzpicture}
\end{document}