Cofermentation of Syrah and Viognier

I read an interesting article in the American Journal of Enology and Viticulture entitled Cofermentation of Syrah with Viognier: Evolution of Color and Phenolics during Winemaking and Bottle Aging.¹
I've heard of the practice of cofermenting Syrah with Viognier and my preconceived notion is that this practice leads to better color retention for the Syrah.
The article begins by mentioning that both Syrah and Viognier are Rhone varieties and appear to be genetic siblings. I went to consult the handy Wine Grapes² and there it was---Syrah is the genetic offspring of Mondeuse Blanche and Dureza and one of the parents of Viognier is Mondeuse Blanche, so it looks like they are half-siblings.
In this study, 100% Syrah was used as a control and Viognier at 3 different concentrations of 5, 10, and 20% during crush was used to test the hypothesis that the wines with the varying concentrations of Viognier would show differences in phenolic concentration as well as differences in color relative to the control.
The various experiements conducted by the authors lead to the conclusion that confermentation of Syrah with Viognier did not lead to any differences in composition of the wines compared with the control. Moreover, when the Viognier concentration reached 20%, this lead to a lower concentration of anthocyanins and flavonols, suggesting dilution of these compounds, which lead to less color intensity. There goes a preconceived notion out the door!
The authors suggest that a future project might involve using pressed skins of Viognier to see if the phenolic contribution from the Viognier pressed skins would lead to better color retention and not to dilution of the anythocyanins from the Syrah and phenolics.
References:
1. Federico Casassa, Landon S. Keirsey, Maria S. Mireles, and James F. Harbertson, Cofermentation of Syrah with Viognier: Evolution of Color and Phenolics during Winemaking and Bottle Aging, Am. J. Enol. Vitic., December 2012 63:538-543.
2. J. Robinson, J. Harding and J. Vouillamoz, Wine Grapes - A complete guide to 1,368 vine varieties, including their origins and flavours, pg 1026, Allen Lane 2012 ISBN 978-1-846-14446-2.