This is a Chinese Bloodroot which I have in a number of places in the garden. It spreads by underground runners and can get to be a bit much sometimes, but is easily pulled out where you don't want it. It is well worth that little inconvenience for its soft green leaves and delicate flowers. Be sure to wear gloves when you pull it because the roots will stain your hands a bright yellow. I'm not sure if it would be a good dye plant, but it might be worth investigating since it has such intense color. I don't usually use natural dyes in my basket making (laziness mostly since it is more work) but this might be fun.
It will grow in sun or shade, though will be more aggressive in a sunnier spot. I don't think it would like full baking sun, though I've never put any in that sort of situation. It is about 8- 12 inches tall with the flowers held above the leaves. The books say that it flowers in spring, and ours usually does, but it also may bloom in the fall which is nice because not much else where I have it growing blooms then.