I have created an environment for my excercises. The problem now is, that if I have different excercises (Excercise 1, Excercise 2 and so on) there is always a little space between them. I have a background color and this is interrupted, so it looks quite stupid. I want to have no interruption so the color is not interrupted. How can I do this? I do not know how to modify the definition of my environment to teach LaTeX to not do any spaces between it....
Here is my code:
\documentclass{book}
\usepackage{geometry}
\geometry{left=4cm,right=3cm, top=2cm, bottom=2cm}
\usepackage[ngerman]{babel}
\usepackage[final]{pdfpages}
\usepackage{xcolor,bookmark}
\usepackage{graphicx}
\usepackage{multicol}
\usepackage[bottom]{footmisc}
\usepackage{shadethm}
\usepackage{amsthm}
\usepackage{amsmath}
\usepackage{paralist}
\usepackage{amssymb}
\usepackage[framemethod=tikz]{mdframed}
\definecolor{aufgaben}{rgb}{0.9333,0.93333,0.933333}
\newtheoremstyle{mystyle2}
{\topsep}{\topsep}{}{}%
{\bfseries}{}{.5em}{}%
\theoremstyle{mystyle2}
\newmdtheoremenv[hidealllines=true,
backgroundcolor=aufgaben,skipabove=\topsep,
skipbelow=\topsep]{aufgabe}{Aufgabe}
\begin{document}
text\\ a lot of text\\
\begin{aufgabe}
the excercise
\end{aufgabe}
%no space here! please!
\begin{aufgabe}
the next excercise
\end{aufgabe}
text\\
ext\\
ext\\ really a lot of text\\ text\\ text\\
ext\\ text\\ text\\
\end{document}
(I know that LaTeX sets the excercises dependend on how much text there is, but also, if the page is full of text there is still a bit space between it, I do not want to have any space between it!)

skipaboveandskipbelow. – Marco Daniel Sep 01 '12 at 07:59\topsepin four places, any of which could have the effect of inserting space above or below the theorem. in particular, theskipaboveandskipbelowinsert space outside the shaded area; i don't know why @HarishKumar deleted his answer, because it would solve at least part of the problem. – barbara beeton Sep 01 '12 at 13:16