Hi Mike,
are you sure that your Roboto Light that you have installed on your PC (or the TTF file that you are using within your project) contains the glyph 0x03C6?
Does it work with other fonts? Just to make sure if the font does not contain the glyph or if your font settings and strings are not correctly.
I just verified it within a HelloWorld example and the Greek character appears as expected.
Best regards,
Manfred.