Hi Maria,

I think that maybe it is Sunburn or Frost-burn (spring desiccation) because of the colder nights/early morning temperatures-a light layer of frost on the leaf may cause this white color.

I do not know why the blue hoasta have uneven coloring although maybe it is the crazy weather cold temperatures swings effecting the coloring of the plants this growing season in the St. Petersburg, Russia. Perhaps?

Quoting the bottom pararaph of this page/link http://www.plantsgalore.com/care/hostas/Hosta-pests-desiccation.htm

"The theory is that the problem is "physiological" which means that it is not caused by a disease or insect. Rather it seems to be caused when the leaves are rapidly expanding in the early spring and the night temperatures drop near or below freezing. High winds or direct sunlight on the plant the next day causes the drying and death of the leaf tissue. The dead tissue then turns a rusty orange color."

Or http://www.plantsgalore.com/care/hostas/Hosta-pests-sunburn.htm

It does not look like HVX virus to me based on these photos:http://www.hostalibrary.org/firstlook/HVXsymptoms.htm

Past forum discussion post by Paul_in_mn with very helpful with good photos:

http://forums.gardenweb.com/discussions/1984263/frost-damage-or-hvx