You can create a class which extends Resources and override the methods getColor(int) and getColor(int, Theme).
Example:
colors.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<color name="your_special_color">#FF0099CC</color>
</resources>
Res.java
public class Res extends Resources {
public Res(Resources original) {
super(original.getAssets(), original.getDisplayMetrics(), original.getConfiguration());
}
@Override public int getColor(int id) throws NotFoundException {
return getColor(id, null);
}
@Override public int getColor(int id, Theme theme) throws NotFoundException {
switch (getResourceEntryName(id)) {
case "your_special_color":
// You can change the return value to an instance field that loads from SharedPreferences.
return Color.RED; // used as an example. Change as needed.
default:
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
return super.getColor(id, theme);
}
return super.getColor(id);
}
}
}
BaseActivity.java
public class BaseActivity extends AppCompatActivity {
...
private Res res;
@Override public Resources getResources() {
if (res == null) {
res = new Res(super.getResources());
}
return res;
}
...
}
This is the approach I have used in one of my apps, Root Check. If you override getResources in your activities and main application class you can change the theme programmatically (even though themes are immutable). If you want, download the app and see how you can set the primary, accent, and background colors from preferences.