Actually, the I only used Paint Tool Sai's Binary Tool for this. The color variations in this are caused by many different semi-tranparant overlay-layers ;)
I can't really see the effects in the picture but you must be using some non-pixel art tools for this to be 128 colors. Try to turn off any antialiasing/blurring effect on your pencil tool.
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Actually, the I only used Paint Tool Sai's Binary Tool for this. The color variations in this are caused by many different semi-tranparant overlay-layers ;)