After running this system on a grid, the concentration can be mapped to some colour values to generate texture. I chose a very straightforward simple mapping:

1. find minimum and maximum concentration values
2. map $x \in$ [min,max] to $c \in$ [0,255]
3. $c = ((x-min)/(max-min))*255$
4. set R = G = B = c

In the above system, mapping the concentration of a to colour gives us dark spots where the concentration of a is high.