Add new 'Use custom background color' to docs

doc/index.docbook

@@ -34,7 +34,7 @@ Context menu actions like Rename Bookmarks etc.)
 			<!-- TRANS:ROLES_OF_TRANSLATORS -->
 		</authorgroup>
 		<legalnotice>&FDLNotice;</legalnotice>
-		<date>2017-08-26</date>
+		<date>2017-10-02</date>
 		<releaseinfo>1.3 (Applications 17.12)</releaseinfo>
 		<!-- Abstract about this handbook -->
 		<abstract>
@@ -2003,17 +2003,14 @@ Context menu actions like Rename Bookmarks etc.)
 					  </para>
 					</listitem>
 				</varlistentry>
-				<varlistentry>
-					<term><guilabel>Obey DRM limitations</guilabel></term>
+                                <varlistentry>
+					<term><guilabel>Use custom background color</guilabel></term>
 					<listitem>
-						<para>Whether &okular; should obey <firstterm>DRM</firstterm>
-							(Digital Rights Management) restrictions. DRM limitations are used
-							to make it impossible to perform certain actions with &PDF; documents,
-							such as copying content to the clipboard. Note that in some configurations
-							of &okular;, this option is not available.</para>
+                                            <para>Enables <ulink url="help:/fundamentals/colors.html">choosing the document background color</ulink> (the color around the displayed page). By default, the &Qt; toolkit color is used when this option is unchecked.
+						</para>
 					</listitem>
 				</varlistentry>
-				<varlistentry>
+                                <varlistentry>
 					<term><guilabel>Open new files in tabs</guilabel></term>
 					<listitem>
 						<para>Whether to open new documents in tabs. The tabs are disabled by default.</para>
@@ -2022,6 +2019,16 @@ Context menu actions like Rename Bookmarks etc.)
 						</para>
 					</listitem>
 				</varlistentry>
+				<varlistentry>
+					<term><guilabel>Obey DRM limitations</guilabel></term>
+					<listitem>
+						<para>Whether &okular; should obey <firstterm>DRM</firstterm>
+							(Digital Rights Management) restrictions. DRM limitations are used
+							to make it impossible to perform certain actions with &PDF; documents,
+							such as copying content to the clipboard. Note that in some configurations
+							of &okular;, this option is not available.</para>
+					</listitem>
+				</varlistentry>
 				<varlistentry>
 					<term><guilabel>Reload document on file change</guilabel></term>
 					<listitem>