To make golden color dosa add very less quantity of sooji (white rawa) to the batter.
Fenugreek seeds/Vendhayam will help dosas getting nice brown color. As per the color needed you can increase or decrease the quantity. This will also make the idli fluffy.
Remember to use only rock salt when grinding idli / dosa. You should not use iodized salt as it will reduce the process of fermentation. Adding enough salt is very much needed for proper fermentation.