(no subject)
The Anglo-Saxons had no word for the common purple-flowering plants which grew by the side of the road all over England (which is strange, since they are found across Europe). As you might expect, they decided to borrow the Latin word, malva, which in Old English came out as mealwe (a reminder, as though you needed one, that Vs in Latin were pronounced /w/). Eventually, by about the 1400s, this became the modern English word mallow.
But! Meanwhile, on the continent, the Latin word had itself been evolving quite a bit too. In the region which is now France, the L darkened and eventually disappeared, Cockney-stylee, so that people were saying maw-va, and by the time they starting writing in the vernacular it was already being spelled mauve. We reborrowed it veeery late, because the colour mauve is quite a recent discovery. William Henry Perkin, the English chemist, was trying to create an artificial quinine, and accidentally made a purple dye instead. He decided to name it after the French word for mallow, because he thought it was the same colour as mallow-flowers. (In fact he originally called it "aniline purple", but worked out that this wasn't very catchy.)
As it happens the French had just about already starting using "mauve" to describe the colour as well as the plant, otherwise they would have been in the embarrassing position of having to instantly borrow back their own word. In French it's masculine if it's the colour and feminine if it's the plant.
Mallow and mauve. Pairs of words like this make me very happy.
Marshmallows, by the way, were originally made from the roots of mallows which grew in marshes. Sounds....kind of hideous.