# Transparency inside empheq (color box)

I'm currently writing a formulary for dynamics and searched for a way to box important equations and have them coloured. The answer to my problem was the empheq package - for now.

Now I'm facing the problem that I would like to get some transparency of my coloured background. Is there any simple implication to my current code or do I need to spend some time in defining a new command?

\documentclass[a4paper,fontsize=12pt]{scrartcl}

\usepackage{empheq}
\usepackage{xcolor}
\definecolor{alizarin}{rgb}{0.82, 0.1, 0.26}

\begin{document}
\begin{empheq}[box = \fcolorbox{black}{alizarin}]{equation}
\begin{split}
I_1\dot{\omega}_1 + (I_3 - I_2)\omega_3\omega_2 = M_1 \\
I_2\dot{\omega}_2 + (I_1 - I_3)\omega_1\omega_3 = M_2 \\
I_3\dot{\omega}_3 + (I_2 - I_1)\omega_2\omega_1 = M_3
\end{split}
\end{empheq}
\end{document}


I could simply change alizarin to a brighter red tone but I would like to keep this colour and just brighten it up a bit so that the text emerges better.

Would mixing some white to your colour do what you want?

\documentclass[a4paper,fontsize=12pt]{scrartcl}

\usepackage{empheq}
\usepackage[x11names]{xcolor}
\definecolor{alizarin}{rgb}{0.82, 0.1, 0.26}

\begin{document}
\begin{empheq}[box = \fcolorbox{black}{alizarin!75!}]{equation}
\begin{split}
I_1\dot{\omega}_1 + (I_3 - I_2)\omega_3\omega_2 = M_1 \\
I_2\dot{\omega}_2 + (I_1 - I_3)\omega_1\omega_3 = M_2 \\
I_3\dot{\omega}_3 + (I_2 - I_1)\omega_2\omega_1 = M_3
\end{split}
\end{empheq}

\end{document}


• Thank you Bernard. This was pretty much what I was looking for. Simple and easy way to brighten up the red tone. – montju Dec 2 '15 at 8:04
• Thank you for appreciating my proposal. I'd suggest using another color for the frame, as it interferes, so to say, with the text. I tried \fcolorbox{VioletRed4}{alizarin!75!} and it looked fine to me. Of course it's a matter of personal taste. – Bernard Dec 2 '15 at 9:57