is red a difficult color to match?

It's cute! I'd wear a white, beige or black top with it. But I think the shape of the top is really important. It would be best IMO if it were something narrow and close-fitting.

I'd choose ballet flats or flat sandals for my shoes.
 
i use red as a "pop" in color. which means, everything else is toned down.

i think a simple white tee/tank would look great and cute sandals.

i LOVE red. when i use red i try not to wear anything else in red so there's no competition.
 
White, tan, and black look great with red. I also really like grey with red. I also like black & white prints (polka dots, floral, etc.) with a solid red skirt.
 
White, cream, navy, brown, tan, black can all look good with red.

I agree... I would wear neturals on top and let the skirt pop on its own. If you want to be more matchy matchy or bold you could wear tops with a little bit of red in a pattern. I wouldn't wear a solid red top with it because it will look like you were trying to match it and it probably won't match.
 
I believe that when wearing a pop of colour (skirt in this case) you should stick to neutral tops. As others mentioned, there are several colours that match with red. Right now I'd go with earthy neutrals (beige, tan, ivory or white), because even though the contrast in red and black looks fab, I don't think it's too good for this season.

Choosing a pattern with a hint of red on your top may also bring the outfit together. Just make sure there isn't too much red on the top or it'll look a bit too match-matchy.

I love the idea of a neutral tank, red skirt, and patterned flats!
 
If you want to add more color I think a pale yellow would look really good. Also navy. A light pink could be cute if you want something more girly. I think you do a colored top your shoes and accessoried should be neutrals. For yoyr shoes, preferably a tan, or something close to your skin tone.
 
for a red skirt i'd go with some type of white blouse on top---i say the more ruffly the better (a la anne hathaway in Devil Wears Prada)

and go with some black patent shoes..doesn't really matter if they're heels or flats usually, but if its a mini i'd go with flats to tone down the hoochie factor