For the color options you have, you can either let the smartness of the script provide a color for you, or you can upload an image that represents that color.
On the Edit HTML/CSS page, locate and click the Assets folder to reveal its content.
Under the Assets heading, click the Add a new asset link.
Upload your image.
Repeat steps 2 and 3 until you have uploaded all your images.
Recommended image size is 55 by 40 pixels.
There's an important naming convention to respect here! The image must be named after the color option, but be handleized, and have a .png extension.
For example, if you have a color called 'Déjà Vu Blue', then name your image deja-vu-blue.png
Other example, if your color is 'Blue/Gray', then name your image
Most simple example, if your color is 'Black', the name your image
For more information you can also check the link below: https://help.shopify.com/themes/customization/products/features/add-color-swatches