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This is my <MyButton /> Component

import React from 'react';
import { withStyles } from '@material-ui/core/styles';
import Button from '@material-ui/core/Button';

const styles = theme => ({
  button: {
    backgroundColor: 'green',
    "&:hover": {
      backgroundColor: "red"
    },
  },
});

function MyButton(props) {

  return (
    <Button
      className={props.classes.button} >
      {props.text}
    </Button>
  );
}

export default withStyles(styles)(MyButton);

Currently, there is the default click effect on the button, brightening/lightening it up on click (see here: https://material-ui.com/demos/buttons/). However, I want the color of the "ripple" to be blue when the button is clicked.

I tried

"&:click": {
    backgroundColor: "blue"
},

and

"&:active": {
    backgroundColor: "blue"
},

No luck though. How do I change the color of the ripple when the button is clicked?

Answers

Here's an example showing how to modify the button ripple for v4 (v5 example further down):

import React from "react";
import { withStyles } from "@material-ui/core/styles";
import Button from "@material-ui/core/Button";

const styles = theme => ({
  button: {
    backgroundColor: "green",
    "&:hover": {
      backgroundColor: "red"
    }
  },
  child: {
    backgroundColor: "blue"
  },
  rippleVisible: {
    opacity: 0.5,
    animation: `$enter 550ms ${theme.transitions.easing.easeInOut}`
  },
  "@keyframes enter": {
    "0%": {
      transform: "scale(0)",
      opacity: 0.1
    },
    "100%": {
      transform: "scale(1)",
      opacity: 0.5
    }
  }
});

function MyButton({ classes, ...other }) {
  const { button: buttonClass, ...rippleClasses } = classes;
  return (
    <Button
      TouchRippleProps={{ classes: rippleClasses }}
      className={buttonClass}
      {...other}
    />
  );
}

export default withStyles(styles)(MyButton);

The default opacity of the ripple is 0.3. In the example I have increased this to 0.5 to make it easier to verify that the ripple is blue. Since the button background is red (due to the hover styling), the result is purple. You'll get a different overall effect if you move to the button via the keyboard since the blue will be layered on top of the button's green background.

You'll find some additional background in my answer here: How to set MuiButton text and active color

The main resource for the styling of the ripple is its source code: https://github.com/mui-org/material-ui/blob/v4.10.2/packages/material-ui/src/ButtonBase/TouchRipple.js

JSS keyframes documentation: https://cssinjs.org/jss-syntax/?v=v10.3.0#keyframes-animation

Here's a similar example for MUI v5:

import { styled } from "@mui/material/styles";
import Button from "@mui/material/Button";
import { keyframes } from "@emotion/react";

const enterKeyframe = keyframes`
  0% {
    transform: scale(0);
    opacity: 0.1;
  }
  100% {
    transform: scale(1);
    opacity: 0.5;
  }
`;
const StyledButton = styled(Button)`
  background-color: green;
  &:hover {
    background-color: red;
  }
  && .MuiTouchRipple-child {
    background-color: blue;
  }
  && .MuiTouchRipple-rippleVisible {
    opacity: 0.5;
    animation-name: ${enterKeyframe};
    animation-duration: 550ms;
    animation-timing-function: ${({ theme }) =>
      theme.transitions.easing.easeInOut};
  }
`;
export default StyledButton;

v5 TouchRipple source code: https://github.com/mui/material-ui/blob/v5.4.0/packages/mui-material/src/ButtonBase/TouchRipple.js#L92

Emotion keyframes documentation: https://emotion.sh/docs/keyframes

Answer demonstrating use of keyframes: How to apply custom animation effect @keyframes in MUI?