I am hardly the target market for painted classic sewing machines, but will offer my opinion here anyway. ...
I have nothing against painting vintage sewing machines but would suggest colors other than neon day glow bright that you might find on a skate board or bike riding jersey. Something rich and deep like a burgundy or mahogany that would really make the gold trim stand out. I just think it would look better on the classic lines of these machines.
Also, the bright colors may contribute to eye fatigue if you actually use the machine for a few hours.