I read this at a website:- "the Su 27 with Model Master II that has colors specific to the Flanker - medium blue, dark blue and blue gray. In service it is said that these colours fade rather rapidly so unless you want to represent one fresh from the depot some diluting with white is in order......"
The web address is http://204.50.25.179/features00/su27dz_1.htm
Another very useful website is this picture intensive one:-
http://www.lindenhillimports.com/48flankers.htm
You're making one of my favourite aircraft (the flanker)
I wish you all success.....
Cheers,
Nandakumar