Thanks for having a look at this and thanks especially for your
comments.

The KML files are generated from a csv file using a java program -
https://github.com/alan-leslie/PsuedoGPSTrace
(I prefer to use KML files because I can check their syntax by
importing them into Google Earth).

I wanted this program to generate the colours used for the themes.
So the colours used in this example have been generated using the MD5
hash of the artist's name.
I agree that some of these are not good for the map.
I reckon that I should set up a palette of colours used in the map,
compare the generated colour to that palettte and if there is not
enough contrast between the colours generate a new one (by shifting
along the MD5?).

Thanks for mentioning the Flickr example, I didn't have a look at it
when working on this (I looked at the polygon tween example instead).
One problem I found when using OpenLayers was that if the polyline
layer is on top of the marker layer a mouse click does not get through
to the marker layer (the comment in mxn.openlayers.core.js is "//
FIXME: click events hitting this layer don't bubble down to markers").
To get round this I try to make sure that the marker layer is on top
of the polyline layer by arranging that the map KML file starts with a
polyline.
So I don't think I could use filters for the polylines.

When I started out on this I actually wanted to make a time map for
the Hundred Years' War that shows the battles and the whereabouts of
the Kings of France and England (that shows that Henry V was at
Agincourt etc.).
I have completed this now - http://bit.ly/IEWEbL.

For this I have had a couple of issues with the timeline which I have
'fixed' with hacks to:
Timeline.OriginalEventPainter.prototype.paintPreciseDurationEvent - so
that the name is shown on mouseover for long timeline tracks where the
left justified label is often not visible.
Timeline.OriginalEventPainter.prototype.paintPreciseDurationEvent and
Timeline.OriginalEventPainter.prototype._findFreeTrack - so that the
English Kings are on the first track and the French Kings are on the
second track.

These hacks are in timeline_hundred_years_overrides.js.

Cheers

Alan