I've been pretty happy with my modded Wombat color scheme, but this is a new one. I grabbed the YAML scheme def file from http://code.google.com/p/pnotepad/downloads/detail?name=yaml.scheme&can=2&q= and dropped it into my /schemes folder. Opening a .yml has highlighting, but it's using the wrong font and I'm not sure where to go to fix it.
http://tivac.com/images/yaml_wrong_font.png
I've double-checked all those settings and they're correctly set to Consolas, but it's very obviously using a different (non-monospace!) font.