Theming: charts use theme text colors.

src/main/java/de/dennisguse/opentracks/chart/ChartView.java

@@ -313,7 +313,7 @@ public class ChartView extends View {
 
         axisPaint = new Paint();
         axisPaint.setStyle(Style.FILL_AND_STROKE);
-        axisPaint.setColor(context.getResources().getColor(R.color.chart_axis_text));
+        axisPaint.setColor(ThemeUtils.getTextColorPrimary(context));
         axisPaint.setAntiAlias(true);
         axisPaint.setTextSize(SMALL_TEXT_SIZE * scale);
 
@@ -322,7 +322,7 @@ public class ChartView extends View {
 
         gridPaint = new Paint();
         gridPaint.setStyle(Style.STROKE);
-        gridPaint.setColor(context.getResources().getColor(R.color.chart_grid));
+        gridPaint.setColor(ThemeUtils.getTextColorSecondary(context));
         gridPaint.setAntiAlias(false);
         gridPaint.setPathEffect(new DashPathEffect(new float[]{3, 2}, 0));
 

src/main/java/de/dennisguse/opentracks/util/ThemeUtils.java

@@ -21,4 +21,20 @@ public class ThemeUtils {
 
         return ContextCompat.getColor(context, typedValue.resourceId);
     }
+
+    public static int getTextColorPrimary(Context context) {
+        TypedValue typedValue = new TypedValue();
+        Resources.Theme theme = context.getTheme();
+        theme.resolveAttribute(android.R.attr.textColorPrimary, typedValue, true);
+
+        return ContextCompat.getColor(context, typedValue.resourceId);
+    }
+
+    public static int getTextColorSecondary(Context context) {
+        TypedValue typedValue = new TypedValue();
+        Resources.Theme theme = context.getTheme();
+        theme.resolveAttribute(android.R.attr.textColorSecondary, typedValue, true);
+
+        return ContextCompat.getColor(context, typedValue.resourceId);
+    }
 }

src/main/res/values/colors.xml

@@ -26,8 +26,6 @@ limitations under the License.
     <color name="chart_power_fill">#40401465</color> <!-- transparent purple -->
     <color name="chart_speed_border">#FF0066FF</color> <!-- blue -->
     <color name="chart_speed_fill">#40C8E0FF</color> <!-- transparent blue -->
-    <color name="chart_grid">@android:color/darker_gray</color>
-    <color name="chart_axis_text">@android:color/black</color>
 
     <color name="holo_orange_dark">#FFFF8800</color>
     <color name="holo_orange_dark_activated">#55FF8800</color>