Help getting purple stems on my seedlings

What causes stems to turn purple? In early veg.

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Strain and genetics. Don't worry about it.

using distilled water will also cause that

Stems turn purple when the temps get too cold for the strain. I've never let it go to the point of the leaves turning. Once the plant gets shocked in that way it stunts the plant and takes a month or so to recover back to a normal speed of growth.