your over thinking it. you cant really notice it. and if you did stain it with concrete stain, you wouldnt have to do the whole foundation, you cant see most of it anyway. put the grass in and live with it. soon enough you will forget about it. paint the door, get new light fixtures...boom attention diverted.

I would plant some flower in front of it.

Even if the concrete was in perfect shape, I would think you would want to plant something there to cover it. So go find some new plants to put there. Don't know where you live, so can't make specific suggestions, but go to a garden center and look around. Other wise it will look boring with just grass. Of course there are also all those really cute statues of gnomes or donkeys you could get....JUST KIDDING. NO STATUES.

soft yellow is nice.

I agree....get the grass growing and let it rain a few times and see what happens to the patch. You will stop looking at it by then and it truly may just disappear.