Roots grow better in the dark. You don't want see-through or white cups. I use peat pots one clones or seeds take root. Peat pots make the first transplant painless. It doesn't stress the plant and there is no danger of damaging the roots. Just pop the peat pot into your next container and your done. Plus the seedling has to work to get through the peat which forces a phase of above ground growth while the roots are restricted which in turn supports increased root development...