It's always the same with Smooth Metallic, its because the place where the edittor is has alot of lightning. If you put your car in the City Garage at the place where the car is in the edittor you'll see what you wanted but if it's not there or anywhere where theres not alot of lightning it looks shit. Theres no fix for this, it's just how it is, as I've had this on multiple cars and colors. Instead I went for Candy Metallic which looks mostly the same as Smooth Metallic but with Candy Metallic you'll get the actual color you wanted everywhere at both night time and day time, Candy Metallic is expensive tho.
TLDR; Smooth Metallic is a bIG scam.