If you want to change a field value to another, we recommend you to use our "Replacer" filed in the wizards" Field Mapping step. Connect your supplier's data feed file to Shopify's fields and click on the gear-wheel to see the settings.
It is especially useful if your text is in a language other than English and you would like to translate some of it, like the color.
You can use the Replacer more than once in case of one Shopify field if needed, just click on the + icon and add another one.
Please note that the Replacer CAN'T REPLACE segments of a value in a field, it can only replace the full text in the chosen field as a whole.