how to tell how many colors in inkscape drawing

You have to do that for each section, so depending how many pieces you have, it might be a lot of work. Using the Node tool, select 2 end nodes, and click either 'Join selected nodes' or 'Join selected nodes with a new segment' button on the Node tool control bar. Or, if you have the pieces already drawn, you can use node editing, with the Node tool, to more or less splice pieces together. Then whatever you draw from there will automatically be part of the last section. Place the mouse inside the square and click once. Or if you draw the outline in a few different pieces, then select the last part that you were drawing, and switch to the Pen or Pencil tool. Then just click once with the mouse inside that square, and the path will be closed. You might notice that the square turns red when the mouse is in the right place. So if you draw one single path, when you're coming back around to the place where you started, you need to place the mouse inside that square. You can only see them while the either Pen/Bezier or Pencil/Freehand tool is enabled.

Did you notice while you were drawing a path, that there is tiny square at the beginning of a path? There's also one at the end of a path. Often it can be done while drawing the path. Often newbies draw paths in pieces, and don't immediately see how to make them connected.

Usually the trick to making a path to be filled with color, it needs to be one, single, closed path.

How to tell how many colors in inkscape drawing