To continue understanding system. in32 and INT in C #: Not chicken or eggs

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After determining "non-chicken and eggs", I was curious about what kind of chicken and eggs they were.

It seems that I was surprised at the beginning why the string and string should be two, but the case is not the same.

So I started a simple test.

On the surface, the colors are different when they are input. String and Int. You enter blue in the default vs style, while string and int32 are pale green. This is just a difference on the surface, but it is absolutely impossible for me to determine that they are exactly the same (even if they seem to work the same, but it is two different entities of chicken (or maybe the same egg from a chicken, but it is divided into two nests. Or one is another colorful "vest ". But it must not be a pair of yellow eggs ).

So I checked it.CodeColor (you can also go to the tool> Option to compare), and specifically change the style to identify and confirm, the results are as follows:
String and INT correspond to keyword.
Both string and int32 correspond to user types.

PS: I am currently using vs2008 only in English. These two references are provided for the time being. Now the problem can be simplified to the difference between keyword and user types (but not necessarily the same. As for the similarities and differences between keyword and user types, I have not found any practical differences. Do you know any of them?