What's the meaning of Nyaa's entry colours?

There are two kinds of colours that appear in each torrent entry in Nyaa's listings:

• One for the rectangle in the "Category" column. I see many different colours there: purple, red, dark and light grey, green, orange, dark and light yellow...

• One for the whole row. Here I've only seen three different colours so far: white, green, red.

Do these colours, especially the second, mean anything?

Nyaa's Help page mentions the meaning of four "torrent colours": green, red, orange, grey. But they don't say where these colours appear. If they mean the row colour, then I've never seen an orange or grey one. So I'm very confused. Maybe the Help page is outdated?

OK, not a life-or-death matter, but I've been curious about this for a long time...