Yes, for ”blå” and ”grå” (grey) you can also keep them as they are in the plural. Both work.
I know this probably isn't the proper place to ask, but I can't find the right place to ask (and it is related) - I want to make a table for myself not to try to learn the gender of every noun but just to drill myself that adjectives have to match the noun's gender, because I always forgot that, for example, "Her birds are blue." is actually a case of adjective (blåa) - so I want to make a table of like - Äpple - ett äpple - det rött äpple - äpplet är rött" etc. Is there somewhere that already has this done, or at least where I can check on all the forms of the sentences I'm writing?
I included all forms in a post here: https://www.duolingo.com/comment/6609356$comment_id=15597433
I do get "You have a typo in your answer." when using "blå" without the extra "a". It is marked 'correct' (as in a green check mark) though.
Blå is singular, blåa is plural. I'm guessing we use the plural form of the adjective because the noun it's describing (birds) is also plural.