YOU SAID:

my fovourite colour is purple and not brown

INTO JAPANESE

私の好きな色は紫で茶色ではありません

BACK INTO ENGLISH

My favorite color is purple, not brown

INTO JAPANESE

私の好きな色は茶色ではなく紫です

BACK INTO ENGLISH

My favorite color is purple instead of brown

INTO JAPANESE

私の好きな色は茶色ではなく紫です

BACK INTO ENGLISH

My favorite color is purple instead of brown