Color of the water on f79v as an indicator of religious cleanliness

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I'd caution against reading too much into it. We don't know who did what coloring or when, what guidelines they followed when coloring, what the manuscript meant to them, and so on. 

As with the plants, we don't know if color annotations were followed diligently, or if the original author(s) had a specific coloring scheme in mind, for that matter. Perhaps that a painter resorted to a secondary color because they were running short of a main pigment.