What do the color codes mean for file blocks?

Solution 1:

The developers change these colors quite often throughout the various updates on the software. Here are the colors that you highlighted;

• Neutral Green: Downloaded and written to disk
• Light Green: Requested data from peers, about to be downloaded
• Dark green: ...No idea as of current moment
• Orange: Canceled Piece
• Purple: Downloaded but not written to disk

There you go :)

Solution 2:

A more correct description of colors:

• Grey: To be downloaded
• Purple: Requested from peer, awaiting download
• Dark green: Requested from multiple peers
• Light Green: Downloaded, not flushed to disk
• Neutral Green: Downloaded and written to disk
• Orange: Canceled Piece