The white uniforms are called your dress whites and the blue ones are your dress blues and you wear them for ceremonies and formal events. For enlisted personell of ranks lower than Petty Officer I believe. Also the white cap is acctually called a Dixie Cup and they arent called caps their covers.

I'm presuming you mean the open-neck jumpers with big square collars and neckerchief and accompanying bell-bottom trousers that are the US Navy's particular variant on a general style worn by sailors all over the world. The history of the US Navy's jumper uniform (like many other Navy traditions) can be traced to the British Royal Navy. The blue jumpers have white "piping" (stripes) around the collar and cuffs, and - although you usually can't see it - the blue trousers don't have a fly but rather a large square flap that fastens with buttons (US sailors often call their blue bell-bottoms "thirteen-button" trousers.) The cap is officially a "white hat" but universally referred to as a "dixie cup", and is unique to the US Navy. Most other Naval services wear a cap with a round flat top and with a ribbon with the name of your ship embroidered on it around the brim. The US Navy used this style with their blue uniform up until about WWII. Generally, blues are worn in winter or cold places, and the whites in summer or tropical climates. They are dress uniforms for ceremonial or dress occasions. The US Navy also has a working or "fatigue" uniform, which when I was in consisted of denim dungarees and a blue chambray shirt, but which I gather has since been replaced. The jumper uniform is peculiar to enlisted men - in the US Navy they are worn by Seamen Recruit (E-1) through First Class Petty Officer (E-6). Chief Petty Officers (very senior enlisted E-7 to E-9) and commissioned officers wear a double breasted suit-coat style uniform with a peaked cap which resembles the uniforms of other services except for color. The uniforms don't have to be "baggy". The military for whatever reason always issues everything two sizes too big. When I was in many sailors got a set of "tailor mades" cut to fit more closely, but baggy seems to be the style nowadays so I don't know if anyone still does this. When I joined in 1975, the Navy had briefly experimented with issuing all enlisted men the sui-coat style uniforms and peaked caps - this is was what I was issued in boot-camp - but they were never popular with the men, and by 1977, the Navy had gone back to jumpers and bell-bottoms. I mean what's a sailor without his "sailor suit'?

Serving in the Navy (southernmost city in the US) quite some time ago - 1963-67 - things may have changed, but this is how I remember it ..... Having worn both uniforms, white - with or without neckerchief - is generally summer, but may be year-round in warm or tropical climates. Blues - with or without neckerchief - are generally for cooler climates, and the blues with piping on the collar, for more "formal" occasions or possibly at the CO's discretion. These are for all enlisted ranks below Chief Petty Officer.