MaterialLoader, opacity affects Spinner and Text

[ingosch]

If background color of the loader and textcolor is the same the text is not visible, also if opacity is 0.5. Is this the desired behaviour? I think opacity should only affect the background an not the other elements of the loader.
This is easy to show in the 2.5.0-rc1 core demo https://gwtmaterialdesign.github.io/gmd-core-demo/#loaders. Check "With Message" -> message is not visible/readable. It only works when "With Background Color" is olso checked.