Where are you located, and what has your weather been like lately?

And are russet mites a problem in your area?

In northern california. There have been a couple of 95 F days here and there but for the most part, day time temperatures have been in the 70s/low 80s while night time temperatures have been in the high 50s/60s.

Most days are sunny but the sun doesn't reach the balcony throughout the entire day. Parts of the plants get ~6 hours of direct sunlight while others only a few. They rest of the day, they get bright indirect light.

Yeah, that could well be russet mites (Aculops lycopersici). Check the leaves immediately above the areas showing damage and discoloration with a strong magnifying class (at least 14x). Russet mites are too small to be seen with the naked eye. They spread in dry, windy weather. If russet mites, then depending on how far the damage has gone, you can try sulfur or, if the plants are heavily damaged, bag them up and dispose of them. http://ipm.ucanr.edu/PMG/r783400111.html

I took a leaf that displayed symptoms and put it under a cheap digital microscope I have. As you suspected, it looks like russet mites (to my untrained eye... please let me know if you think it's something else). Thanks for your help! Will use a sulfur spray to try to extend the growing season a bit.

By the way, do you think it's worth cutting infected leaves?

Yep, that looks like russet mite. The damage pattern is also pretty classic for russet mites I would 100% cut off all dead leaves and any leaves that have started to turn color and, if you can get away with it without totally defoliating your plants, the leaves immediately above affected areas. Bag and dispose, don't let them sit around the garden or put in the compost heap.