problems with new growth??

ive had a plant veging from clone for 6 weeks so that i can take cuttings from it but ive just noticed that they new growth that coming in on the top is starting to get like little rusty coloured dots on it, the rest of the plant is ok ive checked all the underleaf for mites etc and its spotless not a thing whats the cause of these little rusty dots on the new growth has anybody got any idea what it is please help.

I had that happen to some of mine too when I either overwater or actually my perlite was really fine and wasn't drying fully. Also are you using nutrients? I used just water and also started seeing these in my mini bubble cloner on slower rooting clones. So I start using nutes lightly when potted and they either start growing or die, go figure! Good luck.