My husbands greatgrandfather Frederick Mildern was born in Plymouth1822.He married Sarah Rundle in 1841.As a merchant seaman, he lived in Charlton Kent in 1850 and Alverstoke Portsmouth in 1880.Other details are rather scarce.Intrigued by your info. on Frederick Mildern Colston,especially as you say that he was adopted. The only children of Frederick and Sarah are Edward (my husbands grandfather) b. 1856 Charlton Kent and Stratton b.1853 Plymouth.
If you can find any connection it would be interesting