Hallo I'm a novice C# user and I'm not the kind to do tutorials, I'm more of a learning by f... doing.

But this attitude has put me in a bit of a situation.

I'm making a Lab to RGB converter (for those of you who know about colours) so we don't have any compatibility issues around the office (some ppl use open office some use microsoft office, the OS 10 issus ill deal with later).

up til now i'v got it all pretty much running but I am having difficulty getting my output in a textbox.

Ill try to explain. I get an output of 3 doubles and now i need these doubles to follow in succession (an R, G and B value) in a textbox.

I'll add my code and all input, even if it is not an answer, is welcome.
Code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsLABtoRGB
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Double L, a, b, X, Y, Z, var_X, var_Y, var_Z;
            Double ref_X, ref_Y, ref_Z, var_R, var_B, var_G, R, G, B;

            L = double.Parse(textBox1.Text);
            a = double.Parse(textBox2.Text);
            b = double.Parse(textBox3.Text);

            var_Y = (L + 16) / 116;
            var_X = a / 500 + var_Y;
            var_Z = var_Y - b / 200;

            if (Math.Pow(var_Y, 3) > 0.008856)
                var_Y = (Math.Pow(var_Y, 3));

            else
                var_Y = ((var_Y - 16 / 116) / 7.787);

            if (Math.Pow(var_X, 3) > 0.008856)
                var_X = (Math.Pow(var_X, 3));
            else
                var_X = (var_X - 16 / 116) / 7.787;

            if (Math.Pow(var_Z, 3) > 0.008856)
                var_Z = Math.Pow(var_Z, 3);
            else
                var_Z = (var_Z - 16 / 116) / 7.787;

            // Observer= 2°, Illuminant= D65
            ref_X = 95.047;
            ref_Y = 100.000;
            ref_Z = 108.883;

            X = ref_X * var_X;
            Y = ref_Y * var_Y;
            Z = ref_Z * var_Z;

            var_X = X / 100;        
            var_Y = Y / 100;        
            var_Z = Z / 100;        

            var_R = var_X * 3.2406 + var_Y * -1.5372 + var_Z * -0.4986;
            var_G = var_X * -0.9689 + var_Y * 1.8758 + var_Z * 0.0415;
            var_B = var_X * 0.0557 + var_Y * -0.2040 + var_Z * 1.0570;

            if (var_R > 0.0031308)
                var_R = 1.055 * Math.Pow(var_R, (1 / 2.4)) - 0.055;
            else
                var_R = 12.92 * var_R;


            if (var_G > 0.0031308)
                var_G = 1.055 * Math.Pow(var_G, (1 / 2.4)) - 0.055;
            else
                var_G = 12.92 * var_G;


            if (var_B > 0.0031308)
                var_B = 1.055 * Math.Pow(var_B, (1 / 2.4)) - 0.055;
            else
                var_B = 12.92 * var_B;


            R = var_R * 255;
            G = var_G * 255;
            B = var_B * 255;
            
            //THIS IS WHERE I WOULD LIKE HELP
            //THIS IS WHERE I WOULD LIKE HELP
            //THIS IS WHERE I WOULD LIKE HELP
            //THIS IS WHERE I WOULD LIKE HELP
            //THIS IS WHERE I WOULD LIKE HELP
            //THIS IS WHERE I WOULD LIKE HELP
            //THIS IS WHERE I WOULD LIKE HELP
            //THIS IS WHERE I WOULD LIKE HELP
        }

        // numbers only textbox1,2,3
        
        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {   
            switch (e.KeyChar)
            {
                case '.':
                    break;
                case '-':
                    break;
                default:
                    if (!Char.IsDigit(e.KeyChar))
                    {
                        e.Handled = true;
                    }
                    break;
            }

        }
If you see anything you might not do for any reason please tell me. I'm here to learn.