Red Leaves on Blueberry Plants

I noticed that along some parts of the trail there large patches of blueberry plants with dark red leaves. It made me wonder whether this was due to weather (freezing conditions at night?) or if the leaves are always this color.

Location: Harbor Mountain-Gavan Hill Trail, Sitka, Alaska

Previous: Black Lily (Fritillaria camschatcensis)
Next: Unalaska Paintbrush (Castilleja unalaschcensis)