This is a map of Japan from the Cram Atlas which was published in Chicago, Ill, USA in 1899. It bears Taka Isl (which is Argonaut island), Matsu Isl (Ulleungdo) and Liancourt Rocks in the Sea of Japan as usual. And these islands are all painted in light green - the same colour as Oki Is of Japan. The colour of Korea may looks similar but it was different - the latter was printed in longitudinal line while the former was not. [I'm afraid the difference may be hard to recognise on the screen but it is obvious when you look at the real map with a magnifying glass.]
This is another evidence that USA thought that Liancourt Rocks were Japanese territory in 1899 - just one year before the proclamation of the 1900 Korean Edict, that mentioned Seokdo.
[Above is the area of Izumo, Japan. The left is the area of Korea. ]