[m1ckz]

i have a tray of hispi cabbage in cold poly tunnel.......they seem to be going a blue colour  will they be ok do you think  ty

[New shoot]

I have had that with broccoli plants and that was due to a sudden cold snap.  They were OK in the end. 

It has been pretty mild and cabbage is usually very cold hardy, so the other option would be that they need a feed.  Have they been in the tray for a while? 

[m1ckz]

yes  they have  now in 3in pots  ty

[JoshP]

Could be the cold weather or phosphate deficiency

[BabbyAnn]

purple tinge on brassicas is sometimes the result of roots being dislodged (for example, wind rocking)  If you have repotted, it's possible the roots have either been damaged or still adjusting to the new potting media - just remember to firm the soil a little like you would when planting out and heeling them in.  It's not a long term problem and should be fine.