The coral models have rhodium plated solid gold numerals (white) with matching hands on a rose-colored sterling silver dial.
The Martin is most plentiful in the 10K yellow gold filled case. The yellow models also have solid gold numerals in yellow with matching hands on a butler finished silver dial.
The real trick to getting a nice Martin is to find one with the best case possible. Martins seem to wear primarily to the tops of the rounded lugs. The wear can be pretty extensive and it's a challenge to find one without a least a little bit of wear. I had purchased many Martins with worn cases just to get spare movements... as restoring cases is very hard to do.
Under the hood you will always find a 6/0 sized, 17 jewel 987A movement.
The Martin was introduced in 1941, disrupted by WWII, reintroduced in 1946 and made into 1948.
Here's an example of a Martin I once restored. It had a very nice case but the dial was tired looking and needed to be redone.
In the "after" shot you can see there is a little bit of wear through to the bottom lugs. Although the dial looks correct in almost every way, the easiest way to tell it's refinished is the dial plate used to redo these dials is missing the solid zones in the seconds track on the 10 second marks (10, 20, 30, etc). A more proper second hand also completed the restoration.
Here's another example of a very nice Martin I have had. This one's case is also well above average and the original dial is excellent.