Do I need to be worried?

Hello, I have what I’m assuming is a type of coleus I was given in the summer, since it’s been getting colder and the days shorter I have moved it into a vivarium I have made into a type of terrarium that sits around 18 degrees and 60-70% humidity consistently and I open the doors every day to let some of the humidity out and circulate the air better. It’s getting bright light from some grow lights which are about 30-40cm away from the top of the plant
My other two coleus types are thriving, this one is still growing new leaves and growing taller but I’ve noticed on the end of a couple of leaves it is turning whiter? It doesn’t look like powdery mildew, the texture of the leaf hasn’t changed just a slight colour change
I always bottom water and only when the top two inches of soil are dry
I am yet to check the roots but I’m 99% sure they are okay as it’s in a small pot (I got it as a cutting) and none of the roots have started showing at the base holes yet and it’s never been sat in water for too long and there’s no drooping