The salsa bar is an essential part of a good taco stand, at least in my part of the world. Practices vary from place to place but here in Denver the typical taquería protocol is to order from the counter then take your naked tacos, with or without onions & cilantro, over to the salsa bar where you may find many wonderful things to dress them with, such as…several kinds of red, green and orange sauces; radishes; cucumbers; limes of course; jalapeños, pickled or fried; perhaps even a cabbage salsa if you’re lucky. Evry salsa bar is unique, and many of the city's taquerías pride themselves on their salsa bars. The local weekly's annual Best of Denver even has a category for best salsa bar.
Denver is not the only place that's got salsa bars, but they are a signifier of Denver-ness.
My most favorite delicacy to find on a salsa bar tho is those obscene pink pickled onions. (I also like the pickled jalapeños & carrots.) I've been making them at home a lot, with a recipe I got from my mother. Here is her recipe word-for-word, followed by the way I do it:
1 pound firm red onions, thinly sliced
10 peppercorns, lightly crushed
2 or 3 marjoram or thyme branches, or a few pinches dried
Separate the onions into rounds and put them in a colander. Pour the boiling water over them, then put them into a bowl with the rest of the ingredients. Cover and keep refrigerated. The color will begin to infuse in about 20 minutes.
If you want a crisper pickle, you can omit the boiling water step, but it will take several hours for the color to infuse.
I boil 1 qt. water, slice 1 red onion, and pour the water over as instructed above. I take a 32-oz pickle jar, put some oregano, black peppercorns crushed with the side of a knife, red chili flakes, bay, salt, and 1 Tbs sugar in the bottom. Add 1c water, 1c white vin and shake it up. Stuff in the onions and pop it into the cooler. Can be used almost right away and prefrubly within the first few days. After a while they get even pinker and lose their bite.