The colour of an axolotl's gills is somewhat related to level of activity of the axolotl and the level of available oxygen present in the water (warmer water has less).
I think more information on the axolotl's behaviour and environment is needed to give more definitive assistance. For example:
- Is the axolotl active or inactive?
- Is the axolotl gulping air at the surface periodically?
- Will the axolotl take food if offered?
- Examining the gills, do the seem "alive" still - ie, can you still see thin red veins inside them?
In any circumstances, It would be advisable in this case to keep a close eye on the axolotl. If the gill colour change has occured suddenly, then it may revert back to blood-filled quickly too. Just as the human body tends to automatically guide blood to where it is needed most (eg, after eating, more blood goes to your digestive processes than say your arms or legs, and the reverse is true during physical activity), axolotls will most likely periodically have a differing amount of blood in their gill filaments. So don't panic
Also, be careful about the amount of salt that goes into the water. Unfortunately while salt is highly useful for a number of illnesses, it must be remembered that it will not evaporate out of the tank with water, so how much you put in should be carefully monitored.
Therefore my primary recommendation, given what you have offered, is to
a) remain calm,
b) observe the axolotl for a while,
c) do a small water change (maybe 10%?) with dechlorinated water, and
d) watch the temperture. Maybe fill a plastic bottle with water and freeze it, then you can put the frozen bottle in the tank (closed of course) to cool it down.
Good luck, and post back if you have further information.
