Question

What colour is the juice in a Durif grape?

Answer

The juice in a Durif grape is colourless as is the juice in the grapes of all major varieties. The colour in red wine is obtained from pigments contained in the skins of the red grapes, not the juice.
To produce red wine the grapes are usually crushed and fermented with the skins and this process extracts the colour. Red grapes, Pinot Noir in particular, are often used in Champagne and similar clear sparkling wines. To avoid discolouring from the skins these grapes are carefully pressed and the free run juice separated from the skins before fermentation into wine.