Ours are red too. Green toward the middle/newer part of plant and more red on the lower leaves and tips of green leaves. Usually, they get better with cold (live in SC), especially if it snows - makes them sweet.
This year it may be a couple reasons. One is variety. This year we have Georgua collards. Past years have been a 'blue' variety. This years variety seems to have more red as the season progresses, but only I certain beds. Other beds they're still green all around; this leads me to suspect alkalinity. The red ones are in beds where the soil more neutral or alkaline, the green ones are in more acidic soil.