For gold screen wall, you want the DIY column for the value, so: https://mpql.net/tools/acnh/codes/?code=item&item-bytes=8&item-id=16A2&item-slot=24&item-quantity-format=dec&item-quantity=012A&item-durability=&item-keys[a]=a&item-keys[dl]=y
Regarding question 1, I have no idea what you're talking about. Make sure you are specifying the value as 00 so you don't do something weird.
Regarding question 2, yes. Try using customization kits to see if you can change the color. If not, when you spawn one in, color is controlled by the quantity/customization value. Please read the help section that appears when you click a gyroid.
ive got a video that shows the color all funky but dont know how to post it. i usually do 00 but certain times i get weird outputs.