"It is a lovely light gray."
Translation:C'est un joli gris clair.
I think they see 'pale' as a lower intensity of a 'light' color....such as a blue shirt color which is over-worn/over-washed and then becomes 'pale' compared to just a 'light' blue being its own color such as when one buys a brand new light blue shirt. So when Duolingo asks for 'light' (color) use 'clair' and when they ask for 'pale' use 'pâle'!
Go to the Tips and Notes under Colors. It explains why we are using masculine in this sentence.