Who can solve my text positioning problem in my colored tabu header row?

Question

I've a positioning problem in my tabu header. If I define the text color with rowfont, the text in that row will jumping around like a rabbit.

\documentclass[]{scrlttr2}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[ngerman]{babel}
\usepackage{colortbl}
\usepackage{tabu}
\usepackage{xcolor}

\definecolor{TableHeaderColor}{HTML}{444444}
\definecolor{TableHeaderBackgroundColor}{HTML}{EEEEEE}

\begin{document}
    \begin{tabu} to \textwidth {c X}
        \rowfont{\bfseries\footnotesize\color{TableHeaderColor}}
        \taburowcolors{TableHeaderBackgroundColor .. TableHeaderBackgroundColor}
        Header & Test \\ \hline
        \taburowcolors{white .. white}
        Bla & bla \\ \hline
        \rowfont{\bfseries\footnotesize\color{TableHeaderColor}}
        \taburowcolors{TableHeaderBackgroundColor .. TableHeaderBackgroundColor}
        Footer & bla
    \end{tabu}

\end{document}

The resoult is the following:

Update

According to Gonzalo Medina's answer I did this changes:

\begin{tabu} to \textwidth {X[1,m,c] X[9,m]}

The positioning is still not perfect. The baseline isn't the same.

Update #2

After I added \strut as Gonzalo Medina recommended, I've still the problem if I'm using \usepackage{lmodern}.

Answer 1

One option is to change the c column specification; for example:

\documentclass{article}
\usepackage[table]{xcolor}
\usepackage{tabu}

\definecolor{TableHeaderColor}{HTML}{444444}
\definecolor{TableHeaderBackgroundColor}{HTML}{EEEEEE}

\begin{document}

\noindent\begin{tabu} to \textwidth {X[1,m,c] X[9,m]}
\rowfont{\strut\bfseries\footnotesize\color{TableHeaderColor}}
\taburowcolors{TableHeaderBackgroundColor .. TableHeaderBackgroundColor}
Header & Testggg \\ \hline
\taburowcolors{white .. white}
Bla & bla \\ \hline
\rowfont{\strut\bfseries\footnotesize\color{TableHeaderColor}}
\taburowcolors{TableHeaderBackgroundColor .. TableHeaderBackgroundColor}
Footer & bla
\end{tabu}

\end{document}

Depending on you actual needs, the specification might need some adjustments.

A test using TikZ to draw a line showing the baseline:

\documentclass{article}
\usepackage[table]{xcolor}
\usepackage{tabu}
\usepackage{lmodern}
\usepackage{tikz}

\definecolor{TableHeaderColor}{HTML}{444444}
\definecolor{TableHeaderBackgroundColor}{HTML}{EEEEEE}

\begin{document}

\noindent\begin{tabu} to \textwidth {X[1.5,m,c] X[8.5,m]}
\rowfont{\strut\bfseries\footnotesize\color{TableHeaderColor}}
\taburowcolors{TableHeaderBackgroundColor .. TableHeaderBackgroundColor}
Aufwand & Beschr \\ \hline
\taburowcolors{white .. white}
Bla & bla \\ \hline
\rowfont{\strut\bfseries\footnotesize\color{TableHeaderColor}}
\taburowcolors{TableHeaderBackgroundColor .. TableHeaderBackgroundColor}
Footer & bla
\end{tabu}

\noindent\begin{tikzpicture}[remember picture,overlay]
\draw[red] (0,29.5pt) -- (\textwidth,29.5pt);
\end{tikzpicture}

\end{document}