The challenge is getting the patch to look as close as possible to the color of the concrete. With color hardener, this is really easy. Just take a hand full of the same color hardener you used ...

There are so many different concrete patch and repair products out there ... Use one part of cement to two and a half parts ...

looking at it through a screen made with sand, surrounded by buildings made with concrete. I could let you guess what's in concrete, but I suspect you're already catching onto a theme here.