Select just lines in a defined color

Hallo dear friends
In my first trys I was frivolous in handling layers. This had the effect, that I now have outside-lines in several layers and also thickness. The only common is the green color. To change attributes, is it possible, to select lines in one color? I can't believe I have to click on every single line.

Thank youvery much for keeping me sane.

Filtering by attributes not implemented in LibreCAD yet, unfortunately.