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Both Ringo's first solo LP "Sentimental Journey" and Paul's first solo LP "McCartney" were simultaneous in their recordings. Paul was conducting sessions at home, in Morgan Studios and at EMI Studios in London while Ringo was also in EMI Studios during the same month (February 1970) but not at the same time in the same place.
"Blue Turning Grey Over You" was written by "Fats" Waller and a hit for the song was by Louis Armstrong. This song was arranged by Oliver Nelson for Ringo to sing on his "Sentimental Journey" Apple LP. A demo of the song for Ringo was recorded at EMI Abbey Road number 2 at the end of November (28) 1969. Six days later on December 04 1969 at EMI Studio 1. A 17 piece orchestra was recorded and according to studio records, nine takes were produced with the last being best.
Next, Ringo's vocals were added to the backing track. His vocals included a bit of scat singing as well.
Fast forward to February 24 1970 (the same date McCartney was recording "Hot As Sun" at Morgan Studios) and Ringo added more vocals onto the backing track at EMI Studios. Ringo's vocals were layered and edited using six reduction mixes. In total, seven stereo mixes were completed to satisfaction by all. The song was released on the Apple LP/CD "Sentimental Journey".