How does David grow hair?

I can only think that a Technology is there that allows for this.

You would think Synthetics in the real world would come with options for Hair Length and Color that you can adjust when ordering your own Synthetic.    The notion they can grow hair is a interesting one, but i feel it was a lot to do with giving us a David Character that lived as a Hermit and the sense of how long he has been stranded on Planet 4.

It also allows us to see a different between him and Walter, but we can see they could have done this with Blonde David vs Brunette Walter.   However there was always going to be a Switch-a-roo and so how would they do that?

*David finds and has time to Dye his Hair?

*Uploads his Soul to Walter Model?

By having David Grow Hair and him being a Brunette would mean his roots would be Brown and if his Hair grows then over time he would have a certain length of Brown Hair which when he cuts his Blonde Locks off would make him appear like Walter.

Prometheus however clearly shows David Dying his Hair.... if his Hair was Naturally Engineered to be Blonde for that Model he would not need to Dye it, and he was only applying Dye to the Roots, so Prometheus clearly showed us that David Dyed his Roots and thus his Hair does grow.

Considering the overall technology required to make something like David work, I'd be inclined to think that hair growth wouldn't be too far of a leap

its probably programmed to grow at the same rate as human hair. those who designed the earliest models would have wanted to make them as 'human' as possible