The only time to worry is when you see a blue haze within the diamond under certain lighting conditions. This is usually not a problem with medium blue in 90% + of diamonds. Did you see the stone with your own eyes?
My regent is J colour with strong blue fluor and all it has done is made it white white white, Jonathan from GOG (where the stone was purchased from) said that it faces up G/H to him! No hint of yellow face up or pavilion down. The stone is set in a simple 4-prong tiffany-style solitaire that allows me to turn it upside down against a white bg to see 'colour'. Get the opinion of the person who is selling it for you, best of luck!
yes its good an a H id consider it good on anything but maybe a D and even then it isnt really a bad thing.
Med blue should not make any diamond oily looking.
Strong blue will make a diamond look oily in strong sunlight in somewhere around 1%-2% of them with it.
Medium flour. has no negative effect on diamonds ,except...
They usually trade for less money than one's that have none-faint flour.
Also whenever you'll want to upgrade/sell ,it will be used against the stone.