Many thanks to @wmueller (and AI!) for finding a duplicated colour name on this page. ‘lighter bright red’ was used twice. The second version used the right colour information but should have read ‘lightest bright red’ (as it now does!). Fixed image is online and in the images.zip for anyone using aTbRef11 locally.
I’ll confess to my embarrassment that, having checked, this error dates back to the first version of this image that I added in the aTbRef46 baseline back in … 2009! 
Corrections for aTbRef are always welcome. Note: I only make corrections to the current baseline site—at time of writing this is aTbRef11.