Carlos,
Your T55s look great
- which colour did you use?
Thank-you for the links to the decals.
I got quite excited and added some to the shopping cart.
Then I saw the cost including shipping to Switzerland ouch.
I will consider carefully what I actually need. 
Standard Tamiya rattle can TS-28 Olive Drab 2. Funnily enough, I just opened up the box to start on another one (going to open up the loader's hatch this time) and saw that Tamiya suggest TS-28. There's serendipity for you.
The dirtying up is down to Mig and Vallejo pigments. I used to faff about doing Soviet Green but eventually came to the conclusion that most olive greens are much of a muchness and weathering makes up for/ hides most of the differences.
Surprised that postage would be expensive from France to Switzerland. You are next door to each other after all.