A Bridgewood Gardens introduction first offered in 2007.
This is a sport of 'Allegan Fog'. The only difference is that 'Mountain Mist' lacks the dark green border on 'Allegan Fog'. The plant emerges pure white in the spring, with just a bit of green in the throat. Green speckles develop gradually and progressively cover the leaf, as shown in the picture, taken in late June. As the summer progresses, the leaves get darker, until the speckling is no longer obvious. Because there is a significant amount of green pigment in the leaf for a good part of the year, the plant is reasonably vigorous.
The operative term in the above description is "reasonably vigorous". You cannot expect a plant with this kind of coloring to be as strong a grower as a normally colored hosta. It needs plenty of light to do well.
Introduced at about the same time as 'London Fog', which is probably the same plant.