Even after doing a lot of felting, I still have some trouble getting a perfectly smooth outside of a ball using just the wet felting method. If it's small, it's easier, but if I'm maiking a felt ball that I can't completely cup between my hands, I find it's really hard not to get flaps or crevices in the design. What happens is I end up putting another layer of fibre over and finishing it yet again until it looks perfect.
One trick is to make a core in the washer and felt that, then just add the color by hand as a final layer. When you wet the ball, try to keep the color layer as a loose shell without allowing any fibre to double up and form flaps or creases. Hold the ball in one hand and smooth out the creases/felt a tiny area at a time using the other hand--your knuckles or just a few fingers, tightening the wool in the places where it looks like excess is sitting until it's smooth enough to 'full' the entire ball at once (sorry if this is confusing).
Another excellent trick (which works better for me) is to needle felt the colored wool onto the outside of a (washing machine-felted) wool core, and then finish the ball by wet felting. This added step makes the wool stay in place almost totally when it gets wet and your design will work out to be much smoother and easier to hold together. There's a lot less room for error with this method.
As far as colors, in the past I've bought some 'felters candy' from a few different people on ebay and been pretty happy with what I got. There are a few regular sellers with ebay stores that seem to have a good selection and often offer a sample pack for a reasonable price.
Good Luck!
btw where do you buy your rovings from?
