Professional Acrylics come in a greater range of colours and have a lovely smooth, buttery consistency. The translucent binder means they do not darken as they dry in the way most acrylic paint does - making colour-matching much easier. Excellent for impasto effects.
 
Series Numbers: Prices differ depending on the series each colour belongs to. Check your old paint tube or this colour chart to find the series number of the colour you need e.g. Lemon Yellow S2 = Series 2: