Are you doing inventory control? Do you use the same SKU in your store for both items? Are there any changes to price or other details besides the option selection?
There is no standard way, there are a variety of ways and it is generally best to use the one that is easiest for you that fits your application.
Most techniques would involve creating a table to store your options and maybe a second table to group your options, then either adding a third table to maintain the relationship between products and options, or if you would never have a product with more than one option you can just add an optiongroupID field directly to the products table.
This is all assuming you aren't doing inventory control, which complicates the database structure, but begins very similarly.