Thanks for the advice. I think I got the colour scheme from a scan, but it wasn't one I made myself, and I don't think the colours were quite right. I should go back and revise it now that I have a scanner.
Of course, matching printed matter with colours on the screen exactly is hard if not impossible. I don't expect it to be perfect, just to evoke a feeling of nostalgia for the originals.
In any case I'll post the revised version when I get it done, and thank you kindly for commenting. It's so much easier to criticise your maps when you see them through other people's eyes.