How Do I Change The Color Of A Clicked Button Alongside Other Buttons...Supposing I Have A Form With 20 Buttons (4 By 4) And Want That When I Click A Button, The Button And The One To Its Left,...

Create an array of Buttons to represent your button layout, replace MyButton with your button type:

MyButton[,] buttons = new MyButton[4,4];

Whenever a button is clicked, find it in your array (or store the location in the Tag property or your own custom properties, and use offsets to select the other ones, like this:

int x = clickedButton.Row; // Or some other way if you don't have any custom properties in your button
int y = clickedButton.Column;

if (x > 0) MyButton[x-1,y].ForegroundColor = ...; // Or any other color
if (x < 3) MyButton[x+1,y].ForegroundColor = ...; // Or any other color
if (y > 0) MyButton[x,y-1].ForegroundColor = ...;
if (y < 3) MyButton[x,y+1].ForegroundColor = ...;