Although I would've preferred a yellow rasengan. I'm glad Ay's chakra cloak is blue, looks better as blue.The actual colouring of Rasengan is Yellow as it correlates to the colour of the users chakra (hence why Naruto's Rikudou Mode is yellow). The anime coloured it blue as they retconned chakra to that colour (The Raikage's chakra shroud for his V2 is actually yellow in the manga but they made it blue in the anime). But regardless, that wasn't a base rasengan. It was slightly bigger (closer to a Chou Oodama Rasengan) and it was all the remaining chakra Kurama had on top of the rest of Naruto's chakra too.