Is there any way to enforce android.support.v7.appcompat.R.drawable.abc_ic_clear_mtrl_alpha as white color

AppCompat resources can change in future updates. You should put a close button in your resources and use that drawable instead.

If you want to make the current drawable white, then you can apply a ColorFilter. Example:

mCloseButton.setColorFilter(Color.WHITE);

You can also apply a ColorFilter to the Drawable

Drawable closeDrawable = getResources().getDrawable(android.support.v7.appcompat.R.drawable.abc_ic_clear_mtrl_alpha);
closeDrawable = closeDrawable.mutate(); // don't apply the ColorFilter everywhere
closeDrawable.setColorFilter(Color.WHITE, PorterDuff.Mode.SRC_IN);
mCloseButton.setImageDrawable(closeDrawable);

To use your own image, you can use the vector drawable import in Android Studio or get the image from materialdesignicons.com.