Using if statements if Stddraw in java so that you can interact with your code like its a game

Question

int n = 8; // number of rows int m = 8; // number of columns

        // Please do yourself a favour and read the StdDraw documentation
        // https://introcs.cs.princeton.edu/java/stdlib/javadoc/StdDraw.html

        StdDraw.setXscale(-2, m+2);
        StdDraw.setYscale(-2, n+2);
        StdDraw.setPenColor(StdDraw.BLACK);

        // Draw Grid
        for (int i = 0; i < m; i++) {
            StdDraw.line(i, 0, i, n);
        }
        for (int i = 0; i < n; i++) {
            StdDraw.line(0, i, m, i);
        }
       
        StdDraw.line(m,0,m,n);
        StdDraw.line(0,n,m,n);
        
        Color colour0 = StdDraw.GRAY;
        StdDraw.setPenColor(colour0);
      
        // Draw blocks and the gray blocks that the player will interact with.
        for (int i = 0; i < n; i++) {
                StdDraw.filledSquare(0.5, i + 0.5, 0.4);
            }
        
        // Mouse Example
        
        boolean gameIsRunning = true;
        
   //     boolean mouseHack = false; // Ensures that multiple mouse clicks do not occur simultaneously
     boolean mouseHack = false;
        
        while (gameIsRunning) {
               if (StdDraw.isMousePressed()) {
                    if (mouseHack) {
                        continue;
                    }
                    int x;
                    int y;
                    x = (int) StdDraw.mouseX();
                    y = (int) StdDraw.mouseY();  
                    Color colour = StdDraw.BLACK;
                    StdDraw.setPenColor(colour);
                    StdDraw.square(x + 0.5, y + 0.5, 0.4);
                    mouseHack = true;
                   
                 if (StdDraw.hasNextKeyTyped()) { //check for keyboard input
                            char userInput = 0;
                            userInput = StdDraw.nextKeyTyped();
                            userInput = '0';
                            Color color0 = StdDraw.GREEN;
                           
                            StdDraw.setPenColor(color0);
                    }
                     if (StdDraw.hasNextKeyTyped()) { //check for keyboard input
                           char userInput1 = 1;
                            userInput1 = StdDraw.nextKeyTyped();
                            userInput1 = '1';
                            Color color1 = StdDraw.YELLOW;
                           
                            StdDraw.setPenColor(color1);
                    }
                     if (StdDraw.hasNextKeyTyped()) { //check for keyboard input
                           char userInput2 = 2;
                            userInput2 = StdDraw.nextKeyTyped();
                            userInput2 = '2';
                            Color color2 = StdDraw.BLUE;
                           
                            StdDraw.setPenColor(color2);
                    }
                     if (StdDraw.hasNextKeyTyped()) { //check for keyboard input
                           char userInput3 = 3;
                            userInput3 = StdDraw.nextKeyTyped();
                            userInput3 = '3';
                            Color color3 = StdDraw.RED;
                           
                            StdDraw.setPenColor(color3);
                    }
                } else {
                    mouseHack = false;
                }  
           
                }   

}

I want the code to say that if the block is gray (the block is in a "cell") then once the player chooses a color (for example: green or red) then put the color in the block but then also put a gray block in the next "cell". the initial gray blocks are in the first column ("column0"). I have the mouseInput user working already but it works in all cells, it should only work in the gray blocked cells. Please help!!!