I got a bunch of used LEGO bricks from a friend. The bricks were made sometime between 2002 and 2016 when I was not playing with LEGO. I don’t know what set it came from and I can’t figure out what color it is. The square plate is “Dark Turquoise” based on the brick separator being available in that color. This is a darker version of “Dark Turquoise”.
Edited: Thanks for the help. This is a heavily but uniformly discolored blue brick. A chip taken out of it reveals a color of plastic much closer to blue under the surface.