I found the magazine article with the colours.
I used humbrol paints- No:-187 sand , No:-148 Radome and No:- 71 Oak ,these are all matt colours.
They are all mixed in equal part and airbrushed on.
I did not do any washes,it's all chalks/pastels ground into a powder then worked onto the paint.
I did not seal it or touch it again after that but I could imagine if I did it would also lose definition as you found with yours.
However I was happy not to seal it as I was not planning on getting it wet and I thought any extra dust it picked up would naturaly weather it.
For the stop lights.indicators I first painted them silver then went over them with clear red and clear orange.I just kept adding coats until I was happy.
The Tamiya clear colours are excelent for this.They are like a coloured laquer so can look a bit like glass with enough applications.
I have a build thread on this forum of my Sherman that has pictures of my progress.
http://www.rctankwarfare.com/Forums/index.php/topic,253.0.html
Hope this is a help.
Steve.