filling area by color atack safety

i was writing simple editor (something like paint but more custom for my eventual needs) for big pixel (low resolution) drawing
it showed in a minute i need a click for changing given drawed area of
of one color into another color (becouse if no someone would need to do it  by hand pixel by pixel and the need to change color of given element is very common)
there is very simple method of doing it - i men i click in given color pixel then replace it by my color and call the same function on adjacent 4 pixels (only need check if it is in screen at all and if the color to change is that initial color
int RecolorizePixelAndAdjacentOnes(int x, int y, unsigned old_color, unsigned new_color)
{
   if(old_color == new_color) return 0;
   if(XYIsInScreen( x,  y))
   if(GetPixelUnsafe(x,y)==old_color)
   {
     SetPixelSafe(x,y,new_color);
     RecolorizePixelAndAdjacentOnes(x+1, y,  old_color, new_color);
     RecolorizePixelAndAdjacentOnes(x-1, y,  old_color, new_color);
     RecolorizePixelAndAdjacentOnes(x, y-1,  old_color, new_color);
     RecolorizePixelAndAdjacentOnes(x, y+1,  old_color, new_color);
     return 1;
   }
   return 0;
}
it work but im not quite sure how to estimate the safety of this  - incidentally as i said i use this editor to low res graphics  like 200x200 pixels or less, and it is only a toll of private use,
yet i got no time to work on it more than 1-2-3 days i guess but still
is there maybe simple way to improve it?