Minnie's first fiancee, Nixa, described her eyes as "kind, intelligent, animated."
And here Dr. Malcolm Grow, the American surgeon who joined the Russian Army in WWI, described Nicholas' eyes:
"He had large dark eyes---the kindest eyes I have ever seen" (I always like the fact that he wrote this before Nicholas was killed, so you know Grow's memory wasn't tainted by historical events)
Perhaps mother and son did have similar eyes.