colour vectorization parameters

Hi everyone,
I need to vectorize some coloured flat shapes, drawn on paper, scanned and output in Tga.
I can’t find the right parameters: when I use the “-color_vectorize” advanced option, it creates a colour palette containing hundreds shades of the original flatten shape…
I mean, the original drawing has one or two colours, I just need Harmony to create vectorized shapes with these two colours at least.
Anyone can help?
Attached is one of drawings I have to vectorize