Howdy,
If you aren't already, try using warm water; maybe 90-100F so that when it is misted, it will reach her without being cold. She's probably turning dark because she is stressed by the event. If you are using a trigger-type sprayer, switch to a hand-held pump-up type plant mister available at places like Home Depot. Squirt-squirt ends-up more like blast-blast, while the pump-up types give you much more control over the mist pattern and intensity. Keep track of the humidity using a digital temp/humidity meter available at places like Lowe's for about $12.