下面是处理背景颜色的默认ListItem样式部分：

export const styles = (theme) => ({
  /* Styles applied to the (normally root) `component` element. May be wrapped by a `container`. */
  root: {
    '&$focusVisible': {
      backgroundColor: theme.palette.action.selected,
    },
    '&$selected, &$selected:hover': {
      backgroundColor: theme.palette.action.selected,
    },
    '&$disabled': {
      opacity: 0.5,
    },
  },
  /* Pseudo-class applied to the `component`'s `focusVisibleClassName` prop if `button={true}`. */
  focusVisible: {},
  /* Styles applied to the inner `component` element if `button={true}`. */
  button: {
    transition: theme.transitions.create('background-color', {
      duration: theme.transitions.duration.shortest,
    }),
    '&:hover': {
      textDecoration: 'none',
      backgroundColor: theme.palette.action.hover,
      // Reset on touch devices, it doesn't add specificity
      '@media (hover: none)': {
        backgroundColor: 'transparent',
      },
    },
  },
  /* Pseudo-class applied to the root element if `selected={true}`. */
  selected: {},
});

需要注意的重要一点是，所选样式是通过两个类（root和selected）的组合完成的，因此如果您试图使用单个类覆盖它，您将没有足够的specificity。
下面是一个示例，显示了一种覆盖选定和悬停状态的方法：

import React from "react";
import { makeStyles, withStyles } from "@material-ui/core/styles";
import List from "@material-ui/core/List";
import MuiListItem from "@material-ui/core/ListItem";
import ListItemIcon from "@material-ui/core/ListItemIcon";
import ListItemText from "@material-ui/core/ListItemText";
import Divider from "@material-ui/core/Divider";
import InboxIcon from "@material-ui/icons/Inbox";
import DraftsIcon from "@material-ui/icons/Drafts";

const useStyles = makeStyles((theme) => ({
  root: {
    width: "100%",
    maxWidth: 360,
    backgroundColor: theme.palette.background.paper
  }
}));

const ListItem = withStyles({
  root: {
    "&$selected": {
      backgroundColor: "red",
      color: "white",
      "& .MuiListItemIcon-root": {
        color: "white"
      }
    },
    "&$selected:hover": {
      backgroundColor: "purple",
      color: "white",
      "& .MuiListItemIcon-root": {
        color: "white"
      }
    },
    "&:hover": {
      backgroundColor: "blue",
      color: "white",
      "& .MuiListItemIcon-root": {
        color: "white"
      }
    }
  },
  selected: {}
})(MuiListItem);

export default function SelectedListItem() {
  const classes = useStyles();
  const [selectedIndex, setSelectedIndex] = React.useState(1);

  const handleListItemClick = (event, index) => {
    setSelectedIndex(index);
  };

  return (
    <div className={classes.root}>
      <List component="nav" aria-label="main mailbox folders">
        <ListItem
          button
          selected={selectedIndex === 0}
          onClick={(event) => handleListItemClick(event, 0)}
        >
          <ListItemIcon>
            <InboxIcon />
          </ListItemIcon>
          <ListItemText primary="Inbox" />
        </ListItem>
        <ListItem
          button
          selected={selectedIndex === 1}
          onClick={(event) => handleListItemClick(event, 1)}
        >
          <ListItemIcon>
            <DraftsIcon />
          </ListItemIcon>
          <ListItemText primary="Drafts" />
        </ListItem>
      </List>
      <Divider />
      <List component="nav" aria-label="secondary mailbox folder">
        <ListItem
          button
          selected={selectedIndex === 2}
          onClick={(event) => handleListItemClick(event, 2)}
        >
          <ListItemText primary="Trash" />
        </ListItem>
        <ListItem
          button
          selected={selectedIndex === 3}
          onClick={(event) => handleListItemClick(event, 3)}
        >
          <ListItemText primary="Spam" />
        </ListItem>
      </List>
    </div>
  );
}

相关回答：

• 如何覆盖材料ui REACTjs中menuItem中的选定类？
• 如何通过“onclick”事件更改ListItem元素的样式？

• *MUI v5**中可以使用sx prop：

<List
  sx={{
    // selected and (selected + hover) states
    '&& .Mui-selected, && .Mui-selected:hover': {
      bgcolor: 'red',
      '&, & .MuiListItemIcon-root': {
        color: 'pink',
      },
    },
    // hover states
    '& .MuiListItemButton-root:hover': {
      bgcolor: 'orange',
      '&, & .MuiListItemIcon-root': {
        color: 'yellow',
      },
    },
  }}
>

或者styled来创建一个可以多次重用的样式化组件：

import MuiList from '@mui/material/List';

const List = styled(MuiList)({
  // selected and (selected + hover) states
  '&& .Mui-selected, && .Mui-selected:hover': {
    backgroundColor: 'red',
    '&, & .MuiListItemIcon-root': {
      color: 'pink',
    },
  },
  // hover states
  '& .MuiListItemButton-root:hover': {
    backgroundColor: 'orange',
    '&, & .MuiListItemIcon-root': {
      color: 'yellow',
    },
  },
});

现场演示