Have cut 2 clones and the new growth is yellow. There only 2 weeks old and still being fed only water, i'm waiting for roots to show before I put them on half nutes.
also u have to folier feed...so u gotta spray the leaves and keep the clones very humid so that they can get the water and whatnot from the leaves being that they have no roots....iv had this problem many times and my clones died...dont over do it but make sure they stay humid and wet so they can get water from the leaves
Your RW cubes should weigh 25g wet. It is easy to over water them.
Also try a heat mat, but if you use a humidity dome like I do, you will probably get too much humidity. I had to buy a dome with adjustable vents on the top. It works great.