Hi,
The Slavia range are a blued finish. Yours may have just worn away a bit. A bit of info on them in the links below. Very common air rifle in Eastern/Central Europe but not as many examples in the UK.
http://www.czub.cz/en/catalog/84-air..._STANDARD.aspx
http://www.vzduchovka.cz/prehled/85000/85000_en.html
http://www.vzduchovka.cz/prehled/88000/88000_en.html