It’s the reverse of Henry Ford’s line about the Model T.  Today you can buy any iPhone you want, as long as it’s not white.

Apple AAPL has been having trouble keeping the entry-level white iPhone in stock since the new 3GS went on sale two and a half weeks ago. But as of Tuesday morning, it has all but disappeared.

The 16 GB model — apparently the most popular — is out of stock in the 31 of the 41 states in which Apple has stores.

It’s available in only one of California’s 45 Apple Stores, 1 of 9 in Massachusetts, 1 of 7 in Illinois, 1 of 6 in Virginia and 1 of 3 New York City.

It’s not clear whether demand for the white 16GB model is unusually high, or if Apple just isn’t making enough of them.

When we last looked at iPhone availability, there were red “sold out” lights for selected models in all but six states (see here). Today at least one model is out of stock in every state.

The only store in Delaware — located in Newark’s Christiana Mall — is completely sold out.

According to Apple, there are $99 iPhone 3Gs available in all stores, and the 3GS models are restocked “on most days.”

To check availability in the Apple Store nearest you, click here.

AT&T (T) has had 3GS supply problems from Day 1, but Apple’s availability widget doesn’t cover their stores.

Below: A snapshot of the situation in Texas as of Tuesday morning.