Yes, the yellow seedling is due to not enough light intensity, not due to too much light.
If you just placed the seeds in those big holes and did not cover the seeds with extra peat, this is why the other two have not sprouted yet. Seeds need firm contact with the substrate to keep them moist and absolute darkness to germinate. If you did not fill the holes and just dropped the seeds down the holes, they would not be in complete darkness and contact with the moist peat would be minimal, leading to no/poor germination.
All may not be lost just yet, fill the holes with extra peat, keep the plugs moist, but not wet, and warm, and the seeds may still sprout. If it has been longer than 10 days already, starting new seeds might be the way to go. Just remember, the seeds need to be buried and in the dark.
They do not need any sort of "humidity dome" or any other covering, especially cling film, as the seeds need good air exchange also, to germinate, something that is severely limited by using a covering of any sort. Using a plastic "humidity dome" can lead to stretching due to the high air temps and overly humid conditions, which can also lead to mould/fungus attacking your seeds. The plastic also limits the light "through-put", which can also cause the yellow leaves due to the reduced light intensity.
Hope this helps, Organoman.