Sun and Moon: Princess Celestia and Princess Luna

So I made this drawing for the contest of LSeiraL (youtube) the themes were Yin and Yang, Sun and moon and flowers and I tried to use them all. What has this to do with sun and moon? Well, the characters I have drawn are based on Princess Celestia and Princess Luna from My Little Pony. They are like princesses of sun and moon. I drew them in such a way that if you have a lot of imaginary you'll kinda see that it's a little bit of the sign of Yin and Yang. And well the flower theme, I don't really have to explain that...

The sketching+lineart took me about 4 hours and the colouring part 5 hours so that makes a total of 9 hours

I'm still quite new with Sai, so if you could give me some tips for colouring I would really appreciate that
_{But I ask you please... Don't look at the hands, they're a total disaster TT.TT}