I have one (replacement) growing in sun (shade is a premium in my lot) until at least 2-2:30 and it has nice white streaks. It has been in this location for three years now, including 2018.

While it is true that hosta are shade tolerant, I have found that they all grow better, quicker and stronger with at least a few hours of sunlight. Having said that it is all relative to sun intensity in the various zones.

picture taken June 7th... it lost a lot of its blue in the last week during our heatwave.

Good luck with that. If I see a streak I remember it is Spilt Milk. Happens about every other year.

Solution is to get bigger plant from get go and not a TC. The way I am figuring out some plants will have high failure rate during initial growth. This is what Green Mountain sells.

Here's mine 3 year old and also Milkmaid second year