Herb Robert turns from green to red in the leaves. I've read that this can produce a red dye, so have picked some, and steeped some fabric in the liquid.
Unfortunately this plant has a disgusting smell (!) so the house has reeked, whilst I've been working with it. I'm soaking a linen/cotton blend fabric, so it will be interesting to see the difference between this and the thicker cotton fabric I've been using so far.