'The sky looks a pale blue.' 'The sky is a pale blue.' 'The sky looks pale blue.' 'The sky is pale blue.' These are all okay and all mean the same thing. You can use them interchangeably but using no 'a' is more common and there is a slightly different emphasis when you use 'a' When you use 'a (adj.) (color)' 'My shoes are a bright orange.' you turn the word 'orange' into a noun and you emphasize 'bright' There are many different oranges (shades of orange). This one is a BRIGHT (shade of) orange. 'My shoes are bright orange.' is a more straightforward comment and much more common. So usually you would only 'a' if you emphasizing slight differences in colors or if you want to be more dramatic/poetic. A: What color is your new cell phone? B: It's red. A: Is it a dark red or a light red? B: Actually, it's a sparkly red. but it is just as natural to say... A: What color is your new cell phone? B: It's red. A: Is it dark red or light red? B: Actually, it's sparkly red. Easy answer: They are the same.

You usually say : The sky is pale blue. The sky is ( looks or turns) a pale blue color. ( You add here an object). Her face turned pale blue. His shirt turned a pale blue color. In fact there is no difference in meaning and you can use both.