I already looked through the other questions but still could not find the answer I was looking for.
In Sketch, I connect lines to form a triangle. How can I fill this shape with one color? I tried the Union and convert to outlines functions but without any results.
You need to use vectors (shortcut: command+v), and not lines, in order to be able to create the shape and change the color of the fill. By using vectors, you are creating a shape with, essentially, one vector instead of using 3 different lines which to sketch are shapes themselves already.
Here is some info about vectors: https://www.sketch.com/docs/vector-editing/
