@Nick L., @Jay-Bob,
Here are steps to reproduce:
Create a note with two lines of text
Open the color picker (cmd-shift-c) and color both lines of text in a particular color
Select both lines of text and copy
Create a second note and paste in the lines
Select one line of text and using the color picker change it to a different color
Switch to a different note, then switch back to the note in which the color change was made. The color will be reverted to the previous color.
Attached is a screen recording of the issue occurring in Evernote 7.13, Mac OS 10.14.6, with dark mode enabled.