I am suspecting that you are using the image viewer on Windows 10 to view your image. This shows transparent as black and because your text is black it will look like a black/transparent image. When you drag the file into a browser you will see the black logo.
And your color specification is incorrect. When you read the help text of the constructor it will tell you that it expects RGBA. So it should be
And your color specification is incorrect. When you read the help text of the constructor it will tell you that it expects RGBA. So it should be
#FF00007F instead of #7FFF0000"