1. File tools>classify the strings by numbers. The output string ID is the string colour.

1. Open up all the strings in the one layer and save and display with string numbers.

1. Customise>display properties>strings and points. You can set the colour for string 1,2,3 etc.. you can adjust the markers and set the drawing method to MARKER.

1. Save the the styles file as a new name and then save the string file again so it is associated with the new styles file.

Your string file is now coloured by assay, ​​​​​​​