What distinguishes the Bibb variety from Boston lettuce within the Butterhead group?

Bibb tends to be smaller and often develops redder outer leaves

While both Bibb and Boston are classified under the Butterhead umbrella, there are subtle morphological differences that help distinguish them. Boston lettuce is generally characterized by forming slightly larger and looser heads overall. In contrast, the Bibb variety is typically found in smaller heads and often exhibits a specific visual trait: the development of redder outer leaves. These variations in pigmentation, such as reddish hues, can sometimes suggest marginally different profiles of beneficial plant pigments, like anthocyanins, even though both share the core health benefits associated with Butterhead greens.