How to find overlap in a linearized 64x64 array - c

Question

I am working with a linearized 64x64 array. There are either horizontal or vertical lines with "colors" in them set as color codes in each spot in the array, and I am trying to find the color that has no overlap.
An example of what I mean is here: https://imgur.com/a/geE73aK
It is clear that in this example, since none of the yellow are overlapped by any other colors, yellow's color code would be the solution.
It checks left/right and above/below the current position to see if the color is the same. If the color is the same, it will continue. If the color is different (AKA overlap is found), it will make that color code zero and by the end of the program all but one color code will be zero, making it easy to find the non-zero (AKA non-overlapping) color code.
I currently have this as my code. I am stuck on how to find if there is overlap and make the overlapping color code 0. Any help would be appreciated.
#include <stdio.h>
#include <stdlib.h>
#define DEBUG 1 // RESET THIS TO 0 BEFORE SUBMITTING YOUR CODE
int main(int argc, char *argv[]) {
int PileInts[1024];
int NumInts, TopColor=0;
int Load_Mem(char *, int *);
// This allows you to access the pixels (individual bytes)
// as byte array accesses (e.g., Pile[25] gives pixel 25):
char *Pile = (char *)PileInts;
if (argc != 2) {
printf("usage: ./P1-1 valuefile\n");
exit(1);
}
NumInts = Load_Mem(argv[1], PileInts);
if (NumInts != 1024) {
printf("valuefiles must contain 1024 entries\n");
exit(1);
}
if (DEBUG){
printf("Pile[0] is Pixel 0: 0x%02x\n", Pile[0]);
printf("Pile[107] is Pixel 107: 0x%02x\n", Pile[107]);
}
/* Your program goes here */
int i;
int j;
/*
int black = 0;
int pink = 1;
int red = 2;
int green = 3; // all colors and their codes
int blue = 4;
int orange = 5;
int yellow = 6;
int skyblue = 7;
*/
int rows = 63;
int cols = 63;
int colors[] = [1, 2, 3, 4, 5, 6, 7]; // color codes in array format
int current = Pile[i*64 + j]; //current position in linearized 64x64 array
for (i=1; i<63; i++){ //run through 63 rows
for (j=1; j<63; j++){ //run through 63 columns
// CHECK HORIZONTAL OVERLAP
if (current == Pile[i*64+j+1]) //check to the right current position
if (current == Pile[i*64+j-1]) //check to the left current position
// CHECK VERTICAL OVERLAP
if (current == Pile[(i-1)*64+j]) //check above current position
if (current == Pile[(i+1)*64+j]) //check below current position
}
}
//CHECK FOR COLORS WHICH DID NOT OVERLAP - THAT WILL BE SOLUTION, AS THERE SHOULD ONLY BE ONE
for (int k=0; k<8; k++){
if colors[k] != 0 {
TopColor = k;
}
}
}
As for it running from 1-63, that is okay. There will be no colors along the borders.
Clarifying information about the specifics: There will only be one line in each vertical and horizontal. each vertical or horizontal line will be at least one row/column from the other. There will be exactly one color that does not overlap.