Odd one out

After yesterday's taste of spring sunshine, today we were back to the grey skies of winter. I spent most of the day finishing a presentation, but managed a short break for a walk round Thorpe Wood, which was dark, gloomy and surprisingly lacking in interest. Luckily, early in the morning I'd taken an image of this goldfinch, which has been coming to our feeder for much of the winter. It is noticeable paler than the rest of its flock, lacking the warm brown tones that are normally present on the back and flanks. The black, red and yellow feathers seem unaffected, so it's probably a single gene mutation that has caused this variation.