Since ZVTK went to the OTCBB, some brokerages aren't posting the bid/ask. The trades screen keys off the bid/ask. If a trade comes through at the bid price, it registers as a sell. Likewise, if a trade comes through at the ask price, it registers as a buy.
Point to keep in mind -- if you buy at the bid, even though it is a buy, it is registered as a sell. That is why, when a stock is on a tear, you see posts that scream to buy at the ask!! Buying at the bid shows as a sell, or red, and it slows down the momentum. So you are just hurting yourself buying at the bid in that instance.