All I know is that the colored impurities are soluble in water as sodium salts.

Question

so what type of compound does this suggest these impurities are?

Answer 1

It's tough to provide an answer when I don't know the question.
What impurities? What compounds?
But in the absence of all of that I would think you're looking at V, Fe, Mn, Ti, Cr, Cu, Co, Ni salts. Most of those compounds are colored and I think all of the Na salts are soluble.