I think the reason your protocorms "browned out" is because they stayed in the motherflask too long. I just started a flask of some dendrobium anosmum seeds but I added about 2-5 grams per flask of banana puree to the medium. Banana supplies complex carbs as well as simple sugars/glucose for growing protocorms so they stay green even if they have used all the medium in the jar.
I heard from others that when they have enough carbs and sugars and have used all the medium nutrients, they simply pause growth for a bit until they are replated. I added banana pulp/puree and have band-aids on the lids so if the protocorms do become small plantlets or reach a stage where they need to be replated, I should have enough time to replate them without worrying about them "browning out".
Try that next time and see how it goes- I heard coconut milk or coconut water will aid in germination rates and banana can inhibit germination in many orchids, but I must have sown at least 150-350 seeds across the medium. So far it does not look like there is contamination but I will know by the end of the week for sure.