Coloring individual staff lines

Staff lines can be colored independently by overriding the default stencil for StaffSymbol.

The StaffSymbol callback color-staff-lines takes a set of colors (using LilyPond's predefined colors or the functions x11-color and rgb-color) which are applied to each staff line in turn starting with the fifth line (for a standard staff), or each item in the list for custom staves defined with line-positions. To signal that a particular line between colored lines should remain black, use #f.