Many Meconopsis produce albinos and this is the white form of M. horridula (probably the form M. prattii). At least a proportion of any seedlings will be white and in the medium term one can select a plant that breeds true crystaline white.

PLEASE NOTE I HAVE GOT THIS ALL WRONG!

Friends who have traveled widely in the Himalayas and indeed even took me to China to see Meconopsis, say that Meconopsis horridula was broken up by Dr. Grey-Wilson into a number of separate species. These are all quite distinct species and grow in defined locations that are very large distances apart. This is therefore a white form of the species M. prattii. Meconopsis horridula itself has a very wide distribution from west Nepal right up through Tibet and  beyond its borders to the north (it is difficult in cultivation in the U.K.). There are a number of subspecies of M. horridula described, as well as the related M. prainiana, pratti. racemosa and zhongdianensis. For any Meconopsis enthusiast there is a most excellent account with comprehensive and brilliantly photographed images in Dr. Grey-Wilson's book THE GENUS MECONOPSIS from page 238. The book was published by Kew Publishing. Royal Botanic Gardens.
 I suspect many gardeners however will refer to these plants as 'Meconopsis horridula'  as do some major seed lists like those of the Scottish Rock Garden Club. All have really horrid spines which can make seed collecting unpleasant. In the wild there are all shades of blue, pale yellow forms, purple/mauve and pink forms as well as albinos and the anthers vary between bright yellow and white/grey. The spines (very variable) on the leaves may have a purple pigment spot at the base (as does M. rudis in the garden). This like M. prattii is widely established in the U.K. Both are easy probably anywhere and like all this group of plants are usually biennial and monocarpic. 

Meconopsis simplicifolia. This is a photograph taken in the wild by friends in the Himalayas. It does not really do it justice. It is very variable in the wild and it can have really large pale blue flowers that hang down and always single flowers on basal stalks. Dr Grey Wilson in his book on 'Meconopsis'  has split it into 2 sub species. M. simplicifolia ssp simplicifolia and  M.s. grandiflora. When I cultivated them there was Bailey's form and a host of similar ones. Some were definitely biennial what ever you did but others would at least pretend to be perennial though I always found them difficult and lost them. Probably would be easier in cold northern climates. A good large pale blue form is highly desirable and I would love to have it again. It characteristically has blue filaments to the anthers while M . grandis, with which one could confuse it, has white filaments. 

There are quite a number of named species under the basic title of Meconopsis horridula. These range from a beautiful strong medium blue like this through a whole range of muddy purple to white. They have been split into separate species.M. horridula is a high altitude species and very difficult. This M. racemosa in a nice strong colour. Usually biennial and easy from seed and will grow in hot dry places in poor soil. It is very spiny and harvesting seed from very prickly dry pods needs care! Meconopsis rudis is much the same and putting these spiny blue plants into the right species is not easy. Grow from which ever seed is offered to you and then select seeds for yourself and to share with others from the best colour and growth of forms. 

Meconopsis quintuplinervia. Perhaps the most delicate of all the Meconopsis - the harebell poppy. There are at least two forms of this in cultivation which are obviously different. Both have the virtue of being very perennial and easily divided and probably as easy as any of this genera to cultivate.