Dont paint your Blades! Or put any sort of metalic Tape on them!
Blades are really sensitive things, unlike Props, and you may place a great deal more paint on one blade, than on the other(s), and cause a sizeable imbalance creating more damage than mere erosion does.
If you are worried get Blade Erosion Tape as mentioned above, its not great, but its cheap enough, and (if approved for your Type) your mechanic can put the same amount on all blades without too much hassle.
The hardness of your paint also comes into the erosion equation. Cleaning your blades regularly might help you keep an eye on what is happening to them. (and a spot of polish on the top surface really helps generate lift and preserve some of the paint!)