new to AP

[Rolex Rolex]

hi

i am new to AP and i am thinking to buy my first ap watch ..

i have some qustions about ap

what is the different between 15400 and 15300 model ??

i like 39 mm .. but what i read is the ultra thin comes only in 39 mm ,,

what is the dial color you will choose if you are going to buy 15400 ,, white , blue , gray , ??