Font Effects

Hi all,
I'm tidying up the GUI for my project, and I'd like to add a drop shadow to a font, to make sure it can always be read. I imported my font, changed the method from dynamic and had Unity create a PNG for me. I edited that, and it updated it for me.

Problem is, the drop shadow is picking up it's colour from the font, not staying black like in my PNG file. I tried creating a TIFF with a custom alpha channel of just the text, thinking I had fixed it but the results are the same.

Where am I going wrong?

Thanks,
Matt