make SmartWatch work with `transparent` and `currentColor`

[georggrubner]

The two values transparent and currentColor are valid css color values and therefore, the SmartWatch component should not fail with a runtime error trying to parse them.

example code:

const calculatedTheme = {
    ...theme,
    colors: {
        ...theme.colors,
        transparent: 'transparent',
        current: 'currentColor',
    },
}

return <ThemeColors theme={calculatedTheme} />

without those two values, it works fine