Here is the catalog of Suntour BL in 1981. BL was produced for touring bicycle. The group-set was composed of gear sifter, front derailleur and rear derailleur. It was a higher grade model of Load-VX.
The blue fancy plate was put on the pantograph of the rear derailleur. It was an accent of design. However, there was no characteristic part other than that. Since the gear change system was "the slant pantograph" as well as the other series of Sutour.
The first aluminum derailleur of Suntour was V, and the appearance became smarter when Road-VX was developed.
As for the front derailleur, you could detach the inner plate by only loosening the hex bolt. The purpose of it must have been the improvement of the maintenance.

By the way, there was another series Hero which has same design with BL. But it wasn't printed in the catalog at hand.
I had seen Hero at a shop in those days. There was a black plate model other than Blue. Though it was a short-life product, it had been used for middle class mass-production sports bicycle.

Here is the front cover.
Against the background of the horizon, a cyclist was riding a bicycle in the paved road along the seashore comfortably. The catchphrase was expressing that this product was for "touring-bicycle".

Note: the catchphrase said "Blue-new wind BL, extend touring-life".

This is the back cover. The symbol mark of the red triangle had appeared in this year.

The randonneur which was equipped with BL. The catalog was explaining about the trait of BL trait.

Large image of left side.
Large image of right side.

This is the full lineup of BL and the explanation of its trait. Three kind of rear derailleur such as short cage, middle cage, and long cage were prepared. It was suitable for Suntour of those days. Middle cage and long cage were called "Quick cage". You could remove a chain from derailleur without cutting the chain or taking off the pulley. However, there was some trouble; the cage was bent when the chain get over the low gear by wrong setting.
The plinth for the gear sifter was a Campagnolo type. It seemed an exclusive plinth, didn't have compatibility.

Large image of left side.
Large image of right side.