Function rgbToHex

rgbToHex(rgb?): string | undefined
Returns the converted hex color from the given rgb color
Parameters
- Optionalrgb: string | [r: number, g: number, b: number]
  the rgb color to inspect
Returns string | undefined
the converted hex color from the given rgb color
Example
```
rgbToHex('rgb(255, 0, 0)');    // '#ff0000'
rgbToHex([255, 0, 0]);    // '#ff0000'
```