Here are the basic steps I've used to do something similar to this:
1. make 10 different layer files, each for a polygon with one your 10 different colors (or however many you'd like to have)
(set symbology on any polygon feature class in ArcMap to a simple color outline symbol and then right-click and "Save As Layer File")
2. place them all in the same folder and name them "color1.lyr", "color2.lyr", etc.
3. add a color field to each parcel feature and enter the desired color.
4. when adding layers to the TOC with python, use the value in the color field to set the definition query, or use the parcel number if you want separate layers for each parcel. You can then name the layers with the parcel number.
5. use the value in the color field to construct the path to the correct layer file on disk and then use ApplySymbologyFromLayer
Dealing with the various layer objects in arcpy has been a little confusing to me, so be thorough and get ready for some trial and error. I've found it necessary in some cases to use the Layer method to make the initial layer which will be added to the display, and then to use ListLayers to create a "layer as it appears in the TOC" object.
Hope this is helpful,
Adam