Cheese_Monkey:
I'd rather abandon the idea than use a different colour.
A bit melodramatic. Why?
And must any component suggestions be available in the UK? (Even though they are all made in China anyway?)
Instead of the ht16k33, you could drive the displays with shift registers. For the common anodes, you could use MIC5891. For the cathodes, 2 X TLC5916/TLC5917. But the Arduino would have to perform the multiplexing. Not a problem for the Arduino, but more of a coding challenge for a beginner.