https://stackoverflow.com/questions/44827059/syntax-highlighting-with-c/44955728
1.
File -> Settings -> Editor -> Inspection Settings you can turn of color higlighting, maybe it is off 勾选上
2.
Editor->Colir Scheme -> C# ->Methods->Method -> Inherit values from 勾选去掉
3.
有的文件过大，在文件的右上角有个HighLight None， 选择 All 进行高亮