I've tried to look up guides for Feng Shui for this game. Many give details about the correct placements and the luck effects, but I haven't been able to find a list of which kinds of furniture satisfy which color requirements.

Does such a thing exist? Would like to know which things count as yellow or not, etc.

nookplaza.net lists all the colours that each furniture item is classified as. if you click the gear next to the search bar, you can search by colour. that said, I think I remember hearing that feng shui doesn't have any luck effects in this game? not sure if that's true or not

Yep, according to the Japanese guide-book, the Feng Shui luck mechanic is not present in ACNH - "correct" furniture placement just boosts your Happy Home Academy score by 1000 to 1500 points.

I've had feng shui mentioned in a letter from HHA where I was complimented on a yellow piece in my room. I'm not sure if luck is in the game though because I haven't gotten my character to trip or anything else from older games, and also Katrina is not present.

the Feng Shui luck mechanic is not present in ACNH

Honestly thank goodness. Did anyone ever even bother with it much? It would always be in the back of my mind but I want my house how I want it lol

tujunga - Yeah, good riddance! It always bugged me in past games that what I wanted to do with my house and items was curtailed by that mechanic, especially if I had to significantly alter my layouts so as to stop bad luck. Hopefully it will stay gone.

" Did anyone ever even bother with it much?"

Me, right now, right before I made this post. Guess I should have done more research. In fact I was only doing it FOR the luck, my HHA score was fine and is probably tanked now!

A lot of guides out there still say luck is in, presumably because it was in New Leaf and they just assumed it stayed. Ah well!

With my last HHA score they mentioned that I had set my gold fishing trophy to the east which was feng shui, so I think that it does exist, but maybe use the feng shui guide for previous games?

It exists for sure in terms of affecting your HHA score, but apparently in the old games it also affected your luck, meaning you would find rare items, fish, bugs, etc easier.

I would just use a guide form previous games, but there's so much new furniture/DIY in these games that I was wondering if there's any new guides out there. One that says "Here's everything that counts as yellow, here's everything that counts as green, and here's red" yadda yadda.

Seems like I can use that nookplaza to look things up one-by-one? Or maybe I can use it differently, I'm not positive.

^like I said in my post, if you click the gear icon next to the search bar and check off colors, you can search for a colour and find every item that has a variation that counts