Question regarding Worm Castings and Color Change.

I'm new to growing marijuana. I grow in soil and use HPS lighting. I have a few plants at about 6 weeks growing right now. I recently added earth worm castings to my plants. Gave each one the same amount, maybe the size of a seed cup or shot glass. The castings were laid just under top soil. They have been getting the same amount of light, water and air for the entire 6 weeks. After I added the worm castings, the plant changed from a dark normal green to a light yellowish green a few days after adding the castings. Nothing wrong with the plant still looks strong and healthy. I take that this is the (nitrogen?) from the castings. I know the plant color will change back to a darker green sooner or later. Looking to find out if there is a better way to add castings to a plant, so they don't change color?

if you were previously feeding with a chemical fertilizer it would impede the usefulness of the worm castings. regardless.... worm castings have typically a slow release of nitrogen unless used in large quantities /30-40% of the soils make-up(found a lot in organic soil systems). You're plants may be starving, but it's hard to say.. what are you're ph levels like?? more info please.

BTW a shot glass worth of worm castings is like trying to live off of 4 carrots every day. its just not enough juice