Don't forget to skip the extra heat on at least one of those batches also. I think the difference will be obvious. 15 drops per Liter may not be enough to get you the lighter color but if you keep increasing in 5 drop increments you will surely see what I mean by the time you get to 25 drops per Liter.
BUT, don't take it too far. If you do you may run into stability issues. ( colloidal silver would start out looking beautiful but it would change color after 1 or 2 weeks on the shelf.)
So you don't want to go past about 25 drops per Liter if your EL is truly 1 Molar.
Another thing you may not have noticed is @ 10 drops per Liter you were getting a lot of silver dust on the cathode. At 15 drops not as much & by the time you are over 20 drops there is almost NONE. However @ 20 drops & higher your anode will be blacker by end of run which is no big deal. Just fire it off & you're good to go.