Not following any instruction, I just tried to do a complete watercolour painting using this picture.
I did not stick to the colours in the picture (ie. local colours), trying instead to use a simpler palette. Even then, mixing watercolours is hard; I just couldn’t get the grey I had in mind onto the palette.
On a side note, I learnt something interesting while reading up on “watercolours for beginners” sites. It’s not advertised much, but you really have to prime your palette before you put any paint on it (I’m referring to the physical palette on which you mix your paints as opposed to the choice of colours for a painting).
Most new plastic palettes have a film over the top which doesn’t accept water very well, this means that watercolours tends to bead or slide from the surface. When trying to mix colours on the palette, the paint won’t leave the brush, leave it just loaded with colour.
Some suggests scratching at the surface, however that just leaves ugly looking grooves on the plastic which the paint will stick to – and not much else. I find that rubbing at the surface with a tissue (may need some elbow grease) until the surface becomes matt will be sufficient. I was thinking of posting up a picture of my palette, but it’s really quite grotty at the moment XD