No transparency

```
I've been trying to export canvas renderings to png via data urls...
With no background colors / image there is still solid black.

What is the expected output? What do you see instead?

What version of the product are you using? On what operating system?

Please provide any additional information below.

I've used this rather hackish solution where my background color is pure green
and ....

case 'standard':
default:
for(var src=0, dest=0; src> 16;
data[dest + 1] = (color & 0xff00) >> 8;
data[dest + 2] = color & 0xff;
if (color != 0x00FF00){
data[dest + 3] = 0xff;
} else {
data[dest + 3] = 0x00;
}
}
break;
}
```

Original issue reported on code.google.com by `a...@cheong.co` on 3 Sep 2013 at 8:46

Start by reproducing the canvas rendering export to PNG via data URLs, using a rendering with no background color or image. Compare the exported result with the expected transparent output; done means pixels without a background are no longer exported as solid black.

Written by the indexing model from the issue text.