NEW:

How about something like this?
(short version)
All sailor changing to yellow or to white would need a special password you set to change, so you can just keep your guys safe from stealing by turning them from white to yellow. Then, if you want to sell them later on, turn them white by re-entering the pass and sell? This would go well with everyones so far idea.
The not able to dismiss yellow sailor feature would be included in this to prevent anything from happening to them.

(less complicated version)This would  give the ability to turn Yellow saliors into white sailors to make them sellable, and dismissable. And white sailors into yellow sailors to make them secure, this in turn would require a password, a 4 digit (like the HQ pass) or custom pass. (like your pass to log in)  White sailors are still sellable, and dismissable, Yellow sailors would not be either sellable or dismissable, for the reason if someone somehow gets your pass, you will not lose any sailors if they are all put to yellow.
 

OLD:

This odd and annoying feature stops you from tradeing your "noob crew" guys. It should be removed so that all sailors can be sold.
There is no reason I see to keep this feature alive.... All that it does is stop you from trading them.

Here is what i mean, you class a guy, but you want to buy boosted or preimum sailors later.
So, you go to trade room, and you make up a deal to trade your gunners for better gunners, Pilots, etc.
Then you sudden;y notice that you can't do it because they are yellow! This feature has no puropse and  i think it needs to be removed.