Like we have a argument to set the "presplash" we can have a argument to set the background color of the loading screen (sdl2 bootstarp).
Example:
nano -w pythonforandroid/bootstraps/sdl2/build/src/org/kivy/android/PythonActivity.java
...
mImageView = new ImageView(this);
mImageView.setImageBitmap(bitmap);
mImageView.setBackgroundColor(0xFF0000FF); <=== This set the background to blue
mImageView.setLayoutParams(new ViewGroup.LayoutParams(
ViewGroup.LayoutParams.FILL_PARENT,
ViewGroup.LayoutParams.FILL_PARENT));
mImageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
...