I tried that and got told "You need the article "the" here" with the answer suggested as "The wall is the colour pink", which a) doesn't sound natural and b) is at odds with the translation shown in the header for this page i.e. "The wall is pink" ... which sounds natural, but doesn't translate the χρώμα part of the Greek sentence, nor the έχει.

I agree, in English it is perfectly açeptable, but for some reason or another DL doesn't seem to like it: it marked me as incorrect just now when I tried that very answer! :-(}

Corrected ;)