using System;

var red = 51;
var green = 255;
var blue = 51;
var alpha = 128;

var htmlColor = $"#{red:X2}{green:X2}{blue:X2}";
//htmlColor is #33FF33
Console.WriteLine($"style=\"color: {htmlColor}\"");

//with transparency
htmlColor = $"#{red:X2}{green:X2}{blue:X2}{alpha:X2}";
//htmlColor is #33FF3380
Console.WriteLine($"htmlColor is {htmlColor}");