I think grey means it sank due to causes other than you.
As for SS and MV, it goes back to the sailing ship days. At that time British military vessels were separated by type: HMS was a ship, or 3-masted multi-deck war machine. A frigate was HMF, a smaller ship was specifically called HM Sloop. As late as the 1890s the the brand-new Torpedo Boat Destroyers were actually called HMTBD. Merchant ships of the sailing period used SS as sailing ship.
With the coming of steam SS became Steam Ship. MV actually mostly referred to smaller vessels, bigger ones being MS (Motor Ship). Sometimes in reference pages they are further divided into Motor Merchant, Steam Merchant, Motor Tanker etc. Then there are the non-English-speaking types. Norwegian steamships are D/S, for Dans Skib (Steam Ship).
And then there's the use of puctuation. Originally it was S.S., H.M.S., U.S.S. etc. In modern merchant parlance the '/' is sometimes also used: S/S, M/S, M/V and so on. When I started the Ship Names project the convention used in the files was S.S. and M/V. I decided that since it was considered the most common, I stuck with Steam Ship and Motor Vessel just to keep the confusion from becoming too great. Then, because the military versions had long been reduced to no punctuation at all (HMS, USS) I decided to do the same for the merchants, so what you have now is the simplest possible version.
I had several discussions with JScones when he demanded to know what the heck I was doing to his files when I sent him early versions. He was all
and I was all
until we were both
.
Then there's the other problem: All British ships with 'Empire' in the name, and a few others besides, were owned by the Ministry of War Transport. I asked Jim, and he asked his dad for me, if they should be prefaced with MoWT. The answer was no, he only ever heard SS, and that a lot of the time in conjunction with Motor Ships as well. On the other hand a lot of ships were owned by the US Army as transports, and they are prefaced with USAT.
Confused yet? I know I am.
[edit] One of the things Iambecomelife and I are agreed on is how nice it would be to make all the ships nation-specific, so if you sink a ship with a Greek flag it gets a Greek name as well as being the right size and shape. Unfortunately in SH3 that means creating a new model and folders for each new nation for each ship, which means the loading times are going to get even worse. SH4 would be much easier to do that in, but SH4 has been mostly unmodded in those departments.
I have high hopes for SH5 in that realm. We might even be able to make IABL's dream of having them be registry-specific come true, which would mean that the ship you sank that said Lykes Lines on the side would actually be named 'Adabelle Lykes'.