Index: /trunk/src/org/openstreetmap/josm/data/Preferences.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/Preferences.java	(revision 811)
+++ /trunk/src/org/openstreetmap/josm/data/Preferences.java	(revision 812)
@@ -330,5 +330,5 @@
 
 	synchronized public void putColor(String colName, Color val) {
-		put("color."+colName, ColorHelper.color2html(val));
+		put("color."+colName, val != null ? ColorHelper.color2html(val) : null);
 	}
 
@@ -346,3 +346,17 @@
 		return def;
 	}
+
+	synchronized public double getDouble(String key, double def) {
+		putDefault(key, Double.toString(def));
+		String v = get(key);
+		if(null == v)
+			return def;
+
+		try {
+			return Double.parseDouble(v);
+		} catch(NumberFormatException e) {
+			// fall out
+		}
+		return def;
+	}
 }