The "Bovril Boats" were always very smart and actually had black hulls and pale green upperworks. The green cast on the photo above is probably a scanning issue. There were more than three ships though Rick.
Having said that, when the EU put paid to offshore waste dumping in the 1990s only the Hounslow, Bexley and Thames were in service.
As curious foot-note, Thames Water now operate two ships, but their task is in total contrast to these boats and instead of dumping, they inject up to 30 tonnes of oxygen per day directly into the river when the sewage system gets overloaded and the oxygen level falls as a result of raw sewage being dumped directly into the Thames. The two ships are: 'Thames Vitality' and 'Thames Bubbler'
I served on 3 of the Thames water bovril boats until just before dumping was stopped.The Hull was green.They were cracking boats to work on and I hear roumers that Hounslow and Thames are now runing fresh water dow in the gulf.
I drank with the her cheif engineer Barry Dixon in 1988/9, and got aboard for a nose about. She was painted green. Wondering if this is the same hounslow though as i dont quite recognise the configuration. She was beautifully maintained though.