You can use variations to give customers a choice of colour from within one listing (there are also text options to allow for personalisation). You always need to create the complete listing first and list the item. If you then go to the listing you’ll see the option to edit it and also a bit that says ‘add or edit variations’ - I’ve circled it on one of my things here
Click on that and it’ll open a window where you can add your variations - this listing has a choice of 2 colours so I’ve used the ‘drop-down’ variation option and added the colours.
Then you can save your changes (it’ll show you a green button to do that) and go back to your item. There should then be a big orange ‘choose options’ button that your customer will also see. If you click on it you can check that your variations are showing correctly! Hope that helps 