My pickled asparagus with carrots and garlic stayed nice and crisp but they became olive hued during canning.
In my experience, just about anything that starts out green turns brownish green when in contact for more than a few minutes with an acid such as vinegar or lemon juice. Would love to know if anyone has a solution for this! ;o)
I've never tried canning it, but I always set the chlorophyll in asparagus prior to cooking. First shock in heavily iced water to cool the internal temp and slow cooking. Blanch in rapidly boiling water (20 seconds or so) to set the pigment. Shock a second time to stop the cooking process. You could also try adding an alkali (baking soda) to your blanching water, but it might react with your pickling liquid. I would try it with a small amount and then soak the asparagus in vinegar, so you aren't committing to anything. The shock, blanch, shock method will leave your asparagus crisp and vibrant colored. I hope it works!