I think the 'value' house brand's plainness also helps to nudge less price-conscious customers up to the next level up of own-brand stuff. Tesco used to have three levels of own-brand: the blue-and-white-stripe "Tesco value", a more "normal" looking Tesco own-brand, and the premium "Tesco Finest". I suspect the dated plain look of the 'value' range helped it avoid cannibalising sales of the mid-range versions of the same items.