Right now it's lacking the distinct sculptural quality of Helm's work, something which even outside of emulation it would be good to bring in (that is, in general, the face feels a bit mushy).
Helm has quite a few threads explaining how he does things (philosophies as well as methodologies, the former being more useful to know in the long run). I'd suggest grabbing his profile, going to "see last posts", and scrolling through the big ones, as well as looking in general discussion for threads he's started. I know in particular there is one with a wealth of palette discussion which he may or may not have initiated, but contains a rather extensive look into why he picks things.
My memory (and perhaps I'm overlaying my own working too much) is that the colors generally deviate around a central hue (that is, the whole of a region balances out to a specific, usually logical color, most likely a neutral like gray, brown, sage, slate, sandstone, etc), are seldom collected in large/distinct enough quantities/shapes so as to become autonomous (that is, they remain part of the greater, rather than creating color shapes, even in pieces where the color shapes are prominent), and tend towards secondaries.
