toHex method
- int value
 
Converts an integer value to a hexadecimal string.
value: The integer value to convert, which should represent one of the RGB color components.- Returns: A string in hexadecimal format, with a leading 
$and two digits. 
Implementation
String toHex(int value) {
  return '\$${value.toRadixString(16).padLeft(2, '0').toUpperCase()}';
}