The parsleys are yellow because they are overcrowded and competing for nutrients. Do those containers have drainage holes? If not, and they were in the rain, they could be waterlogged.
The problem with sowing them so thickly is that you'll often destroy the roots trying to separate them. Instead, separate them into clumps of several seedlings, plant the clump, then clip off all but one or two of the healthiest green sprouts with scissors — don't try to separate each little sprout. You'll lose all but a few, so if you have more seeds, sow them now, well spaced.
