I would say that its mildew. You can treat it with a fungicide but as they are young plants, I would use a more dilute mix. Having said, how long have you had these plugs? It could be that they had become infected before you received them. So if it is just a short time then I would get back to your suppliers with a complaint.

also reduce watering and improve air circulation around them.
some do have a light 'furry' appearance though.

But if you have only had them a fortnight or so then perhaps contact your supplier.

Thank you jimmytheone, for your advice.

I think its my fault SBG, I have had them about a month, do you think I should put them outside during the day? thank you for your advice.

I wouldn't put them outside as even cold winds will damage them at this time of the year.

No far too cold at the moment. try and space them so there is about 12" between each plant.

Thank you so much both of you for your help.

Depending on how thick the "fur" is it might be a case of mealybugs.