假设您使用的是 material-ui-next，您可以在createMuiTheme 中使用覆盖。

import { MuiThemeProvider, createMuiTheme } from 'material-ui/styles';

const theme = createMuiTheme({
  overrides: {
    MuiInput: {
      underline: {
        '&:before': { //underline color when textfield is inactive
          backgroundColor: 'red',
        },
        '&:hover:not($disabled):before': { //underline color when hovered 
          backgroundColor: 'green',
        },
      }
    }
  }

});

然后用MuiThemeProvider包装你的应用程序

ReactDOM.render(
 <MuiThemeProvider theme={theme}>
   <Root />
 </MuiThemeProvider>,
 document.getElementById('root')
);

它将覆盖所有 TextField material-ui 组件的下划线颜色。如果您只需要为一个 TextField 更改颜色，请使用https://material-ui-next.com/customization/overrides/#1-specific-variation-for-a-one-time-situation

Rinat 的回答似乎不适用于当前版本 v16.13.1。使用borderBottom而不是backgroundColor.

（借用他的回答使答案更清晰，希望我没有违反任何 SO 准则）

import { createMuiTheme } from "@material-ui/core/styles";

const theme = createMuiTheme({
  overrides: {
    MuiInput: {
      underline: {
        '&:before': { //underline color when textfield is inactive
          borderBottom: `1px solid ${"red"}`,
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        },
        '&:hover:not($disabled):before': { //underline color when hovered 
          borderBottom: `2px solid ${"red"}`,
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        },
      }
  }
}

并像以前一样用 MuiThemeProvider 包装它：

import { ThemeProvider } from "@material-ui/styles";

ReactDOM.render(
 <MuiThemeProvider theme={theme}>
   <Root />
 </MuiThemeProvider>,
 document.getElementById('root')
);