Here is a video on how to set up product options such as size and colour within Infusionsoft
With Infusionsoft each product can have up to three option types. Colour and Size would be two options.
Within each option you can have unlimited choices.
You can also have different pricing for different options. The way it works is by adding or subtracting from the base price. For example a product may have a base price of $15 but if you want an XL size then that option has a +$1 adjustment giving a final price of $16. A Sm size could have a -$1 adjustment so it's price would be $14.
Here is a video explaining it all.