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I would wait and watch carefully and frequently until the color fades back to a more green hue. If the color goes clear then huge amounts of plankton are dying - and or dead. The color going from green to brown can indicate the phytoplankton ran out of nutrients, then a change to Brown is often due to very high numbers of zooplankton blooming to eat the phytoplankton bloom. Brown to clear is often all the zooplankton ran out of food and starved to a quick death. All the dead biomass consumes lots of dissolved oxygen to contribute to fish suffocation. The brown color change could be due to a shift of plankton species that are adjusting to the lack of rain and water evaporation and the changes of dissolved chemical shifts in the water that determine what plankton species are growing best in the pond. Chemical shifts are occurring constantly in the pond, some are and become big changes. Biggest DO concentration sags most often happen in the early morning before or at sunrise. Note that some algae species when they are abundant will create color hues in the good condition water including shades of brown. It all depends.
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