As you may already know - Shoji Kawamori was the chief designer of MP-03 Starscream. He is also well-known for his mecha designs and anime designs for Macross, Diaclone (which later became Transformers), and also Convoy Hybrid (THS-01 & THS-02).
When Takara came to Shoji with the Masterpiece Starscream project they gave him lots of free range in the design. Shoji was adamant from the beginning that he wanted to design a realistic looking jet, and the robot mode would be secondary.
His visions and adamancy led to a perfect looking F-15 Eagle which included intricate details on the fuselage, nosecone radar, wing flaps, and airbrakes.
Shoji was also insistent about Starscream's color. Again, he wanted a real looking jet, which is why he chose the gray. In Shoji's opinion, he feels that Starscream's robot mode contains enough red and blue to recognize him as the character. It was not asked if an Anime colored version of Starscream would be released in the future.