My beardie who's over a year old has been brumating for the past month, we live in Australia so it's winter here. She sleeps for 5-7 days then wakes up. She's recently just been sleeping in and gets up. I dunno what's happening she's so random I dunno if any things wrong. And a few days ago it was about 18 degrees Celsius on her cool side coz she's usually sleeping hard and doesn't wake up but she was a dark grey and awake when usually she's a bright yellow and asleep. I don't know if she wanted to wake up but it was too cold. I just dunno what to do!?
It really just sounds like your beardie is brumating, and it appears to be normal. My youngest bearded dragon is a golden yellow color, but when it's nighttime, not the warmest, and she's sleepy she turns an ashy gray. Like, she becomes 100% gray with no touch of yellow in her.
Bearded dragons will be fine as long as the temperature of the enclosure doesn't drop below 60 degrees at night (I'm not sure what that translates to in celsius). If it is dropping to a really cold temperature, I would recommend getting a ceramic heat bulb. These don't emit any light so they can be on at night and still keep the enclosure all cozy and warm!