Yes; if you would like your clients to have the choice of purchasing Black & White or Sepia colored prints through your storefront, follow the steps outlined below to enable those option:
From the main menu click Selling » Prices, Shipping, Tax » Pricing Sheets.
Click on the name of your pricing sheet .
Check the box in the B&W and/or Sepia column for each of the purchase options you want to offer those color choices for.
Click Save Pricing.
Note: this option only affects prints, it will not have any effect on downloads. Downloads will be in whatever color you originally uploaded your images in.