[avhon1]

FWIW, the FLOSS CAD program SolveSpace can generate parametric sketches and export them as SVG files (file > export 2d view)

[WillAdams]

Is there a facility when doing this for controlling colour/fill?

[avhon1]

SolveSpace does have some ability to control the color and fill of areas. It's nowhere near as powerful as Inkscape, but enough to make simple diagrams. The exported SVGs can also be edited in Inkscape.