in Thoreau’s Journal:

At Corner Spring Brook the water reaches up to the crossing, and stands over the ice there, the brook being open and some space each side of it. When I look from forty to fifty rods off at the yellowish water covering the ice about a foot here, it is decidedly purple (through, when I am close by and looking down on it, it is yellowish merely),

while the water of the brook and channel, and a rod on each side of it, where there is no ice beneath, is a very beautiful dark blue. These colors are very distinct, the line of separation being the edge of the ice on the bottom; and this apparent juxtaposition of different kinds of water is a very singular and pleasing sight.