I can't find how the user can change the color of text added by the user.
If I add a text field in th UI Designer, then I can change the text color on the product page but if I add a new text field (with the add text button) on the product page then there's no way to change the color.
What am I doing wrong?
If you go to your WooCommerce Product and click on individual product settings in the meta box of fancy product designer you can click on the tab "custom text properties" and there you can enter the colors your customers can choose from. Entering only one color code enables the color picker.
Is it posible to have swathes to limit the colors?
yes you can set the colors in the individual product settings in your WooCommerce product.