Practice is vital in mathematics if you want to develop. I imagine this is the same for everything but particularly so for maths. It comes down to attention. We all have very limited powers of attention and working memory. To do maths of any complexity requires that some parts of it are automatic. The skills that we need to make automatic in the first instance are things like simple addition and multiplication facts. (Well we often call them simple, but they are not. They are simple if you remember them and then don't ask any more questions about them but they can be difficult if you either don't remember them or you do ask more questions about what they mean.)
Let's break down a mathematical task which might be complex to those who haven't mastered certain skills - long division.
A long division question might be presented as 4567 ÷ 7. The first thing that you would do is put it into long division format - the first hurdle. You might know how to do that easily (you wouldn't with out some practice)
Long division involves repeating 4 procedures for each column in the number you are dividing. The procedures are:
If all of these procedures are automatic (i.e. you can evaluate a multiplication like 6 x 7 with out much effort) then it is still quite a long process. If these procedures are not automatic then this is a real struggle if not just impossible.
So the purpose of practice is to make procedures automatic so as to facilitate further and more complex mathematical procedures. The purpose of Prime Colours is to allow you to recall arithmetic facts automatically and flexibly.
This can be clearly seen in a game like Prime Colours - Spot it!, Link 25 or Connect 4