I found a really good way to try and figure out what colours you need is to import the image in to GIMP image editor (free open source image editor) and use the Color Picker Tool, tell it to "sample average" and set an appropriate radius (if you only sample a point it's hard to get a guesstimate of what you actually need).
The darker brownish areas of the dog are approximately this colour:
http://www.colorhexa.com/94563a
The darker parts of the creamy areas are approximately this:
http://www.colorhexa.com/dbc5b5
So look for paints that match those swatches. I would say based on
GW's colour swatches, Skrag Brown is probably the closest out of the pot to the brownish colour... but I don't trust
GW's colour swatches, I have no idea what Skrag Brown looks like when it's actually painted.
Out of Vallejo's range, the closest to the brownish areas is the Model Colour "Orange Brown". You can use this to get an estimate of what Vallejo colours might be close:
http://scalemodeldb.com/paint
The creamy colour to me looks like Rakarth Flesh, but that might be a bit too faded, I dunno. I'd be tempted to start from something darker and work my way up.