Struggles with Paint

WHY WONT PAINT COVER EXPANDING FOAM CORRECTLY!

I am really struggling today to find a way of painting expanding foam fully, for more than one reason! 

Trying to paint acrylic or emulsion paint to stick to expanding foam is difficult, it takes 3 or 4 layers before getting a good coating. I have tried spray paint but this covers the knitting and adds colour to the knitting and this is not what I want to achieve. I have tried painting each nodule one by one but it is very time consuming and its not a productive way of working. 

I have worked by leaving some areas with no paint on, over time these untreated and unpainted areas with change colour the more they are exposed to light. 

I know this is only a short post but im starting to get really frustrated and beginning to think if painting the surface is the correct thing to do.