diff --git a/quad9/hw_preamble.tex b/quad9/hw_preamble.tex
index dfa8f4c..e5522aa 100644
--- a/quad9/hw_preamble.tex
+++ b/quad9/hw_preamble.tex
@@ -68,16 +68,27 @@
 
 \newcommand{\separator}{\noindent\hfil\rule{0.75\textwidth}{0.4pt}\hfil}
 
+% Versió impresora:
+\newif\ifprintversion
+
 \newenvironment{Problem}{%
     \stepcounter{problem}%
-    \begin{tcolorbox}[colback=cyan!10!white,parbox=false]
+    \ifprintversion
+      \begin{tcolorbox}[colback=white!10!white,parbox=false]
+    \else
+      \begin{tcolorbox}[colback=cyan!10!white,parbox=false]
+    \fi
         \textbf{Problema \theproblem.}~%
         \setcounter{solution}{0}}{%
     \end{tcolorbox}
 }
 
 \newenvironment{FreeProblem}{%
-    \begin{tcolorbox}[colback=cyan!10!white,parbox=false]
+    \ifprintversion
+      \begin{tcolorbox}[colback=white!10!white,parbox=false]
+    \else
+      \begin{tcolorbox}[colback=cyan!10!white,parbox=false]
+    \fi
         \setcounter{solution}{0}}{%
     \end{tcolorbox}
 }