I specially looked up the Cantonese dictionary. The word "Guo" has no other pronunciation. According to the landlord's description, it seems to be like the word "Guo" of glutinous rice cake, and the dark green cake mentioned seems to be like "Ai". Perhaps the landlord saw the variant of "Guo" like "Guo", and it is awkward.

adding green pigment to white powder will turn green ...