Different white winemaking by-products (pomace, skins, seeds and stems) were compared as natural sources of phenolic compounds having biological and sensory properties of oenological interest. Antioxidant and copigmentation effects of these by-products were studied in wine-like model solution. RRLC-DAD was used to establish differences on the phenolic composition and the ABTS method to compare the antioxidant activity. Spectrophotometric and colorimetric analyses were performed to asses the magnitude of copigmentation and the changes induced in the color expression of red wine anthocyanins. Antioxidant and copigmentation properties significantly varied depending on the type of by-product, which was related to their qualitative and quantitative phenolic composition. Seeds and pomace showed the highest antioxidant potential while skins and pomace led to the strongest and visually perceptible color effects on red wine anthocyanins by multiple copigmentation (darker, more saturated and vivid bluish colors). Results open the possibility of technological applications for the wine industry based on re-using winemaking by-products to improve the biological value and color characteristics of red wines.