const style = {
  play: {
    margin: 5,
    padding: 0,
    colorInherit: 'linear-gradient(45deg, #38e438 30%, #58e458 90%)',
  },
  play_disabled: {
    margin: 5,
    padding: 0,
    background: '#222',
  },
  clear: {
    margin: 5,
    marginRight: 10,
    padding: 0,
    background: 'linear-gradient(45deg, #FE3B3B 30%, #FF3B3B 90%)',
   },
  clear_disabled: {
    margin: 5,
    marginRight: 10,
    padding: 0,
    background: '#222',
  },
  default: {
    margin: 2,
    padding: 0,
    color: '#fff',
  },
  disabled: {
    margin: 2,
    padding: 0,
    color: '#777',
  },
};
const theme = createMuiTheme({
  palette: {
    primary: {
      main: "#777",
    }
  }
});
<MuiThemeProvider theme={theme}>
  <Tooltip title="Render" placement="bottom-start">
    <Button
      id="play-btn"
      variant="outlined"
      size="small"
      onClick={this.handleRender}
      color="primary"
      className="header-btn"
      style={this.props.layoutType === layoutTypes.REFERENCE ? style.play_disabled : style.play}
      disabled={this.props.layoutType === layoutTypes.REFERENCE}>
      <Icon className="material-icons" style={{ color: '#777' }}>play_arrow</Icon>
    </Button>
  </Tooltip>
  <Tooltip title="Stop" placement="bottom-start">
    <Button
      id="stop-btn"
      variant="outlined"
      size="small"
      onClick={this.clear}
      color="primary"
      className="header-btn"
      style={this.props.layoutType === layoutTypes.REFERENCE ? style.clear_disabled : style.clear}
      disabled={this.props.layoutType === layoutTypes.REFERENCE}>
      <Icon className="material-icons" style={{ color: '#777' }}>stop</Icon>
    </Button>
  </Tooltip>
</MuiThemeProvider>