John,
The ones on my Carlton were blue. Prior to that I had a Y reg Rang Rover
that had similar Monroe on the back - the Boge strut thing was aparantly U/S
and the previous owner had fitted the Monroes as a cheaper alternative. And
they were blue, too.
The Carlton had a valve hidden under the carpet in the corner of the boot
area, just inside the O/S rear lights. The valve was just like a tyre valve
and any forecourt airline (or foot pump) could be used. The Rangey was a
similar arrangement with the addition of a pressure guage. Monroe used to
sell an onboard compressor with a dash mounted switch to inflate/deflate the
shocks.
My current Ford Explorer has a very similar set up. Dunno if it's by Monroe
but the system is fully automatic - ride height is maintained regardless of
load. If you are interested I have a spare set of Explorer hardware -
shocks, compressor, ride height sensor, some valves and other gubbins. Note:
The Carlton shocks have much more 'travel' than the Explorer shocks. In fact
IIRC the Carlton rears have more travel than Rangey rears.
Thing is, I don't see how this type of shocker can help a serious trials
machine. OK, they can be used to raise the ride height - but in that case
you'd have them pumped up to the max all the time so you might as well just
fit longer spring hangers or parabolic leaves or longer coils or whatever is
cheaper.
If you are anywhere near Cleckheaton, West Yorks you are more than welcome
to see the Carlton and Explorer shocks in the flesh...

Simon H