Hi.
I would like to be of help but I don't really know how to. Can I just say I like it?..
Wait. I know. Maybe you could eh, give some more shading to the hair? I don't quite understand the shadows and highlights in the hair (regarding the color I mean). I think, I'm not entirely sure.
Anyway, pretty good drawings, these look quite proffessional, given what I've seen on your website, your shading with regular gray pencil seems much much better. (By the way, the site is only in spanish?)
Did that help? Or was I just saying stuff without knowing haha, because that's entirely possible.