Unfortunately, this information is INCORRECT. Please refer to AbdallahSmash's YouTube video on Feng Shui for correct information. The system was changed between games.

Clarification:
With "right" Area, i meant "correct area" not the right side.
So green items to the south, red to the East and and yellow to the west.

Every room gets their own set of points.
Once per color but for each room. Duplicate items don't count.
Set ONLY 3 items on the right area of one room for full color points, build the rest as you want. Do the same for the other rooms. Don't use the same items for different rooms. It will not work

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Does this count for all rooms or just the main floor of rooms??

I have had lots of luck

The Luck part is actually not true. The official guide mentions, that luck is not being affected anymore, unlike in older games.

I think there are also some other things that changed. But i can't remember what else.

Does it work with flowers? If I put a red tulip would it be red or green?

How do you know what furniture is which color? do you have to eyeball it or does it tell you?

In the above text, "Judging range is 2 squares on the wall side", does this mean 2 squares from the wall? Does this include the wall as well?

I believe it applies to all rooms.

Does this only apply to the main room in your house? not the additional rooms?