theme-provider.js

import { ThemeProvider } from 'styled-components';

const theme = {
  primary: PRIMARY_COLOR,
  error: ERROR_COLOR,
};

return (
  <ThemeProvider theme={theme}>
    <App />
  </ThemeProvider>
);

...

// usage in a styled-component
const StyledTitle = styled.h1`
  font-size: 1.5em;
  text-align: center;
  color: ${props => props.primary};
`;