Can you help me match this grout?
Unfortunately, no. If you read the Wikipedia article on color balance you'll learn that it is actually quite difficult to maintain true color when capturing and displaying digital media.

For instance, the article has a pair of renderings of the same image of a lily:



The left image is as-shot by a digital camera; the right image is adjusted so that a gray surface in real life would appear as gray in the image. You'll see that the images are clearly different, but even that's too simple, as the author of the image couldn't account for your (or my) web browser and computer display, which will likely further tamper with the color rendering.

Your best bet is to continue working as you have been, and if you find no match close enough for your taste, figure out how to manufacture such a match by either blending different colors of grout or feathering the edges of the patch.