I do not understand the question, sorry. What images? What stains? What are you trying to find out?
"Intensity" of stain is not a reliable measure of product quantity unless you know the staining is stoichiometric (and DAB is not so).
If NBT is a chromogen (I can see that NBT is a type of cell too), you need to determine the colour vectors using the method descibed in the website Ellen has provided. You can input the vector values by adding it to the colourdeconvolution.txt file that is present under the /plugins folder (if you are using Fiji)