Niceboxes (latex)

This nice sty comes from an example I found on the web. The code is not mine. However, I wasn't able to find again the original code (and the original author) to give credit. There may be some small modifications I made: if it does not work, it's likely it's my fault.
You can define things like

\usepackage{niceboxes}
\newenvironment{definition}[1][Definition]{
\par
\SpecialEnv{#1}{LightSlateGrey}{Lavender}{LightSlateGrey}{}%
}{%
\endSpecialEnv
}

Of course you need to have imported xcolors if you want to call colors by name (like LightSlateGrey)