Yes, that's right. I'm trying to follow the evolving software development model. Which means that each new release should have all the advantages of the older version and some new features.
If you like, all versions, apart from djviewer-b-0.0.3b are obsolete.
djviewer-bw had only the black and white layer, which has the highest contrast but sometimes if you see a picture you will not see it in full quality. sometimes only a few lines. So the Version 3b has the feature that you can then select the gray mode and few the picture in full grayscale and then switch back.
djviewer-margin was basically the djviewer-bw version just with one adjustment when you zoom to fit the width of the page.
Actually, the version 3c is in development which includes a more intuitive way of selecting the layer to be displayed. I had to think of this more intuitive way as on the 302 I had no cursor keys available and couldn't select the menu option to select the layer.
So I developed a mode were you select the layer by tapping into one of the corners. E.g. top left corner means full grayscale and the screen will be immediately updated. bottom left is foreground layer and bottom right is black and white.
This is really far more convenient then going through two menus to select the rendering mode. After I played with the 302 a bit I really started to love this easy way of selecting and accordingly I will add this feature in a similar way for the 90x, 60x series in the next version.