This is a colour used by artists. As Jenni says, "lake" has nothing to do with a body of water; it denotes the type of pigment called lake, in which a dye is combined with a white binder. In the case of lake white, however, there is no dye; it is just a white metallic salt, namely alumina hydrate, also known as aluminium hydroxide, with the formula Al₂O₃·3H₂O or Al(OH)₃.

Here is an account of its chemical composition:
Nicholas Eastaugh et al., Pigment Compendium: A Dictionary and Optical Microscopy of Historic Pigments, p. 15.
http://books.google.es/books?id=P7vbXHR2mTYC&pg=PT67&lpg=PT6...

"ALUMINA WHITE OR LAKE WHITE
This is the hydrated oxide of alumina which is ground in linseed oil, and is almost as transparent as glass. It is simply used as a medium for reducing or attenuating other pigments as, for instance, when it is desirable to glaze with burnt sienna, it is of advantage to mix burnt sienna with alumina, because in that way the burnt sienna assumes all the qualities of a lake color. Alumina is permanent, and is not affected by other pigments. As however, the amount of oil necessary to grind alumina into the paste form is very large, the oil contained in the mixture is prone to turn yellow. It has a variety of advantages, however, which makes it exceedingly useful and can be generally recommended." (p. 88)
Maximilian Toch, Materials for Permanent Painting
http://www.ebooksread.com/authors-eng/maximilian-toch/materi...

As the name "transparent white" implies, lake white or "blanc de lacque" is also combined with other colours to produce a transparent pigment.

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Note added at 2 hrs (2012-11-05 21:54:24 GMT)
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Unfortunately the subscript doesn't seem to have worked in the chemical formula: Al2O3·3H2O or Al(OH)3.