lavender in greenhouse going red

I have grown some lavender from seed last year and potted the seedlings on into larger pots of multi purpose compost and grit. The greenhouse is unheated i assume the reddening of the leaves is due to the cold. Also i have noticed some brown patches have developed on the lower leaves which i presume is a fungal attack. I have put them outside to give them more ventilation and presumably will need to spray them with fungicide.