You can get a suprising amount of control with watercolours. Personally I build up thin layers of paint which gives you both the translucent value of watercolours but with vibrancy ‘cos they CAN look wishy-washy sometimes.

I often use the lifting technique to fix mistakes: I put water on the mistake only – the rest of the paper is dry and the kitchen paper I use for lifting is dry. Sometimes I use a dry brush for the lifting. Doing this you can almost get back to the white of the paper, and it doesn’t look muddy unless you are repeatedly fixing the same area. Personally I find muddiness is reduced dramatically if you do not use the black from your palette, instead mixing brown and blue to create it yourself. This ‘black’ is easier to lift and more forgiving.