Was the year 1978?In 1978 the Policia Armada became the Cuerpo Nacional de Policía and were redressed in brown, so they were subsequently knicknamed "maderos" (piece of timber) specially by delinquents.
I visited Spain in January 1979, and I remember seeing police dressed in light-grey uniforms with old-fashioned closed collars having a diamond-shaped red badge. They also wore rather flat grey peaked caps with a red band.
The border guards (or Customs officers?) had a similar uniform, except that it was green. The police on the street in Madrid had a blue uniform.