isHexColor function
can starts with or without#
must contains
Implementation
bool isHexColor(String? input) =>
input != null &&
(RegExp(r'^#?([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$').hasMatch(input) ||
RegExp(r'^#?([A-Fa-f0-9]{8}|[A-Fa-f0-9]{3})$').hasMatch(input));