t = page:GetCMYKFill()
page:GetCMYKFill() returns the current value of the page's filling color. page:GetCMYKFill() is valid only when
the page's filling color space is #HPDF_CS_DEVICE_CMYK.
This function returns a table with the following fields initialized:
CYMKAll fields contain values between 0 and 1.