Woocommerce - define default options variation tab

General information for the website: Online wool shop
Description of requirements/features: I am looking for a solution to either be able to display 1 variation in two different ways on product page or have 2 variations with only 1 variation required to be selected in order to be moved to shopping cart.

In my case I have some products in my shop that have more than 50 colours available and I would like my customer to be able to select either by colour (image) OR by colour number (dropdown). Ideally I would like to work with only 1 attribute that can be displayed in two different ways but the only way to have both options on my single product page I found so far was by creating two attributes. The problem is that you also have to select both in order to add this item to your cart (see:http://www.wollyhood.nl/product/paris-recycled-denim).

I was told that default options can be defined in variations tab but I have no clue how and would appreciate some help.

If you like to see an example of what I am looking for: http://www.wolplein.nl/wol/stylecraft-wondersoft-merry-go-round-dk
In this case only 1 selected option allows you to place the item into your cart (the dropdown menu automatically updates to the correct colour variations when clicking on a picture).
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