From what I can tell, the A indicates silver and the J indicates gold. Maybe one of the watchmakers,
@Archer ,
@Canuck or
@Horlogerie can shed some light.
This shows you can't rely on Cousins numbering system, as it does not reflect Omega's. A silver day wheel, black lettering, in English is 72207501516A, so that is the part number you need.
A yellow (gold) day wheel, black lettering, in English, is 72207501516AJ.
A pink day wheel, black lettering, in English is 72207501516AR.
So the first letter at the end indicates the language, and the lack of a second letter defaults to silver with black lettering. If there is a second letter, it indicates something other than silver with black lettering.
The number for the gold one from Cousins appears to have left off the A, so if you needed an English in gold, I would suggest calling them because each language will have a version with J for the colour and you would want to make sure this one is actually English.
Letter codes for the languages:
A for English
B for Arabic
D for German
E for Spanish
F for French
H for Dutch
I for Italian
K for Danish
L for Finnish
P for Portuguese
S for Swedish
T for Chinese
Cheers, Al