I buy full or part fleeces when I like the look of the colour. Although I do clean the fleece and wash the hand spun you will still find plant matter in the yarn. If you think some is too thin just snap and rejoin.
My yarn is called thin an d slubby for a reason. I love to see texture in anything so make sure my yarns have finer parts and then blobby bits, or slubs.
I generally use 4mm or 3.5mm to knit it up.
 
Leo 9 balls - tan
Teal  0 balls -browny black
Limelight 9 balls  -dark grey
Heidi 5 balls - light brown
Beauty 10 balls - one of my favourites as lovely and soft -off white
Basil - 0 balls - black
Seamus - 6 balls, currently spinning this fleece so more to come. white
Sunray - 5 balls, a local alpaca, lovely and soft ginger brown.
Angus currently being spun 2 balls
Totally Random - 5 balls. This is always different as when I have insufficient fleece for a 50 g ball it gets put in a bag. Every so often I spin from the bag. It can be more of any colour so cannot be colour matched.