I have made it my personal rule that photochemistry does not mix with kitchenware. Some compounds in color developer are quite problematic and with heating you always create vapour. Unless you have a dedicated microwave for this I would strictly advise against heating your chems that way. Note, that the microwave will heat your chems unevenly, so you may end up with areas where your chems are much hotter than they should get while other areas are still cool. Remember, you can't stir in a microwave!
The way I have been heating my color chemistry without any of these problems can be described quickly:
- Grab a bucket big enough to hold the bottles you store your color chemistry in
- Fill it with hot water (50-60°C) from the tap
- Put the bottles with your color chemistry into the bucket, make sure the water level stays a few cm below the liquid level inside your bottles, otherwise they might float and tip over.
- Open the bottle with the first solution you are going to use and put the thermometer in
- Wait until it shows the desired temperature and start processing
- Leave the other bottles in the bucket for another 1-2 minutes, then take them out and dump the water from the bucket
- During these 1-2 minutes they will gain some higher temperature, and by the time you need them they will have cooled back down a bit. Since the temperature of the second (and possibly third) bath is much less critical you should be fine without further adjustments.