color-interpolation

Consider the following document:

  <svg xmlns="http://www.w3.org/2000/svg">
    <rect width='200' height='100'/>
    <g fill='white' fill-opacity='0.5'>
      <rect width='100' height='100'/>
      <rect x='100' width='100' height='100' color-interpolation='linearRGB'/>
    </g>
  </svg>

Should the right half of the rectangular region be a different colour
from the left half?  IIUC, the use of ‘color-interpolation’ should
affect how the right white <rect> is composited into the black <rect> in
the background.

Batik, Opera and Firefox all show a uniform #808080 colour in the
rectangular region, which makes me wonder if I’ve used the
‘color-interpolation’ correctly.

-- 
Cameron McCormack ≝ http://mcc.id.au/