Question about blending options in Photoshop

[dullrazor]

So, Im doing my own textures and the like... just starting out. Im fairly good with photoshop, but I don't know how well those skills will transfer over. My questions are simple really:

I really don't know how to turn something that is in color... white. I mean, i know desaturate or black/white, and I normally up the brightness with comparable contrast. Is there an easier way?

Secondly, I've always used the multiply (well, among others) in my options in a new layer (normal, multiply, overlay...etc etc) so as to keep the integrity of what's underneath (you know how doing "normal, basically just colors OVER the whole thing, right? Well, in at least normal images). I was wondering if "Normal" blending or whatever will keep the detail in terms of textures.

EX: If I use "normal" to color ganon's hair, will it just make a big blob of color (blue, for example), or will you still be able to see his "dreads" as it were?

Thanks in advance.