You had posted other pics of the mare before she foaled that made me think she was silver bay, not chestnut, and filly looks silver black to me, too.
You can go thru many posts here that demonstrate different shades of silver bay and silver black.
Here's a pic of a colt that we own that IS NOT chestnut... Both his parents are tested homozygous black and sire never sired a "red" foal... Dandy is a homozygous black, silver bay tobiano (also homozygous for Tobiano)... He has a single bay gene from his dam and a single silver gene from his sire. If he EVER completely sheds out this summer, I will post new pics of him. This one is from December 2013 and he is 4 months old. The only "proof" or sign of silver is that "spritz" of "smoke" (flaxen!!) in his forelock and bridlepath area and the "smoke" around the outside of his ears. When his bridle path is clipped, a lot of it will disappear. His other points are hidden by white markings. The ear/bp shot was taken just hours after his birth.
Currently we own 13 silver blacks - some pinto (1 with overo characteristics), 2 silver bay pintos, 1 solid silver buckskin (not tested) and 1 solid smokey silver black (not tested)... We've also had a few others over the years - you can see many pics of them here with color changes thru the seasons from birth to now...
PurplePaint Pony Gallery
The solid silvers are: Ami, Bell, Bit, KoKo
The "painted" silver blacks: Bunny, Classy, Cupid, Flashi, GG, Koalah, Rio, Shamrock, Stuffy,
The "other" silvers are: silver bay - Dandy and Flower; smokey silver black - Ranger; silver buckskin - Taff.
ALSO - Iggy, Rocket and Wyndy are silver black tobianos. Iggy was our silver black tobiano stallion that sired all of our silver foals except for Ranger and GG. For us, he only sired one colt that did not have a silver gene - Rocket's full brother, Comet. We no longer own Iggy, Comet, Rocket or Wyndy.
The easiest way to prove to yourself what color your baby and your mare are is to have them tested. We use
Animal Genetics out of Florida - we get the tests back via email w/i 48 hours and usually have the paper copies w/i a week of sending in our samples. There are several other genetics companies that test for silver as well. Otherwise, just enjoy them!!
The filly is really cute and I look forward to seeing how your mare thrives under your care now that you own her.