I don't get it. Why is it not "grønne"? I thought that when the noun was definite (which it is, since we use "DIN mad"), we should use the plural form...
Grønne is for plural green objects. Grøn is for -en singular objects (objects that would end with 'en'. So the man is manden, the green man is den grøn mand) Grønt is for -et singular objects (such as the water 'vandet'. The green water 'det grønt vand')