Good question, so far we have 5 screen densities : xxhdpi,xhdpi,hdpi,mdpi,ldpi , now if you have an image resource you will need to create 5 copies of it, its always recommended to start by the xxhdpi till you reach to the smallest,
however you can use online calculators that will calculate the PX and DP for all the densities, i recommend these two tools android developer toolbox and developers tools, and with developers tools you can test the colors, and how are they going to look like in the screen in HEX decimal.