There are a number of ways of achieving this, depending on the products
imagine you have a table in your database called items.
in items, you could have 12 rows of data, one for each design/colour combination.
if there are essentially 3 designs, which are identical, except for colour, i would have 2 tables, one with the 3 designs, and a linked table with the 4 colours.
further to this, you could have 3 tables, one for the basic watch, a separate one for the design and a third for the colour.
how you decide to do it is dependent on trying not to have any redundant data, ie not have the same information entered several times.
Ultimately, the 'relational tables' model is most flexible, but takes a bit longer to master.