Assuming they are both applied properly, and that the pigments are the same, the difference in appearance is nil.
The difference between acrylic and enamel is in how they behave.
Acrylics dry rapidly, but cure slowly, and do not develop full adhesion or strength until fully cured. They also require a CLEAN surface for application.
There is a wealth of information in these forums on this subject (I know 'cause I put a lot of it there) as well as other scale modeling forums. I suggest a thorough search here and elsewhere.
There is an appreciable difference between different brands of acrylic hobby paint. Check that out, too.