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If she's acting completely normal, doesn't seem uncomfortable or distressed about her ears now, then odds are that it's just a change in pigment and nothing to worry about.
Dogs can have pigment changes their whole lives, and although it is most noticable in the color of the nose from black to pink or vice versa, but it's not unusual to see changes elsewhere on the skin such as the skin on the abdomen or the pads of the feet.
ISince things like thyroid problems can cause the pigment to change, it would be a good idea to call them in the morning and see if they had ever tested her thyroid, and if not, if they think it's something worth investigating, but really don't think it's anything that you need to be concerned about, or need to rush her to the vet for.
I hope this helps.