Hi. :) What is e621's policy for detailed color tags? For example, do we tag white sneakers as white footwear, white shoes, and white sneakers?

I could go for color tagging any and all significant articles of clothing and objects — "significant" being the operative word. Is this appropriate behavior? How many color tags are too many, if there's even a limit?

Finally, are the answers to these questions already documented someplace?

I think it's OK to tag the colors of everything.

sneakers implies shoes and if you check the implications of white_footwear on its wiki page, you can see that white_shoes is among them.

So probably you should tag white_sneakers, white_shoes and white_footwear together.
Ideally, white_sneakers should imply white_shoes, so that everything can be tagged automatically.