Hey Lenny
I have for you, a very interesting website that you may go to to find out pretty much ANY little tidbit of info there is on the Battle of Midway. The website is: www.midway42.org
It is awesome. There also is a roundtable that is posted every two weeks thereabouts and it is FILLED with all sorts of info from military experts, BOM Vets, just an unbelievable amount of stuff.
I think to answer your question, that Yes the numbers were on the decks but in a very subdued color like black or a tad different shade of dark blue. You could post this question on the BOM forum, (It costs NOTHING to join) and you'll hear from a bunch of CV-5, CV-6 and CV-8 vets who were there and could give you first hand info.
Try it, you will get a lot out of it.
Regards,
Freddie from LI