There can be two color palette layers with the same color

as seen in this example:

Using glyphs2ufo produces this output:
```
Bad Color Bold: Glyph A, layer color.0: Duplicate glyph layer name
Bad Color Thin: Glyph A, layer color.0: Duplicate glyph layer name
```
and this layer mapping (it appends a '#' to make the name unique):
```
com.github.googlei18n.ufo2ft.colorLayerMapping


color.0
0


color.1
1


color.0 #1
0


```

So it is not sufficient to use GSLayer.name as layer names in the ufos.