Let them dry out all the way for a couple days and keep an eye on them. Seedlings are very susceptible to a myriad of issues that can stem from overwatering, it's one of the top noob mistakes I see here.

Make sure they are DRY when you stick your finger in down an inch or so before you water again. Container weight can tell you a lot about water in the medium. Fill an empty cup with dry soil and feel it. Then compare it to your grow containers. It should feel oddly light when you need water.

Just a stupid question here, did you make a bunch of holes in the bottom of those cups? Please answer yes, if not that's likely the culprit. Cannabis roots need plenty of oxygen in addition to water. If you don't have proper drainage then it will get stagnant in the bottom of the container and starve roots of oxygen or start to rot them.

Also, sometimes when plants grow quickly the new growth will often come in much lighter than the older growth. The chlorophyll hasn't had time to react to light yet, it will darken in a day or 2. Observation I have noticed that is sometimes confused for a problem.

Just thought it was worth mentioning.