tailwindcss/src/plugins/backgroundColor.js

import _ from 'lodash'
import flattenColorPalette from '../util/flattenColorPalette'
import withAlphaVariable from '../util/withAlphaVariable'

export default function() {
  return function({ addUtilities, e, theme, variants, target, corePlugins }) {
    const colors = flattenColorPalette(theme('backgroundColor'))

    if (target('backgroundColor') === 'ie11') {
      const utilities = _.fromPairs(
        _.map(colors, (value, modifier) => {
          return [
            `.${e(`bg-${modifier}`)}`,
            { 'background-color': value },
          ]
        })
      )

      addUtilities(utilities, variants('backgroundColor'))

      return
    }

    const utilities = _.fromPairs(
      _.map(colors, (value, modifier) => {
        return [
          `.${e(`bg-${modifier}`)}`,
          corePlugins('backgroundOpacity')
            ? withAlphaVariable({
                color: value,
                property: 'background-color',
                variable: '--bg-opacity',
              })
            : { 'background-color': value },
        ]
      })
    )

    addUtilities(utilities, variants('backgroundColor'))
  }
}