Rob
Issue now solved many thanks. Here is what I did based on info provided by you.
I went to metalvortex.com, here I followed the instructions and set the GFX-colour management from the default of 2 (Enable color management for tagged graphics only. (Default)) to 1 (Enable color management for rendered graphics)
Now my robin looks the same in both large and small versions.
I've learnt a lot about colour management over the past few days. Fingers crossed that my brain will be able to retain this knowledge.
Again many thanks for your help in solving this problem.
Harry